There were some big positives for me there — notably the ease of sharing links with people, the way I quickly built up a collection of contacts (many of whom I knew before, many of whom I didn't) with posts that interested me on art, mathematics, and politics, and the level of immediate feedback I got from the +1s and comments on my posts that was much stronger than I've been getting on LiveJournal. For me it hit a happy medium between LJ (where I mostly feel I have to say something substantive to make a post) and twitter (which I follow but where the 140-character-per-post limitation seems too limiting for me to post). I ended up posting a bit more than one post per day, mostly external links with a sentence or two of description, compared to my rate here which is close to one a week.
One negative for me is that, like LJ's friends, G+'s circles conflate too many unrelated concepts: they describe the sets of people whose posts you want to read, they describe the sets of people who can read your posts (so far both like LJ) but they are also used by some people to filter different subsets of their posts to the people they think might be interested in that subset (something I think they work very badly for, because the audience should be choosing which topics they are interested in, not having that choice made for them by the person making the post). When sharing a link, Google automatically chooses the text to describe the link and doesn't let you edit it, and you can only have one nicely-formatted link in a post. And when a post on Google+ gets shared by someone else, the discussion thread gets split up into two places, neither of which is conveniently linked to the other.
But those are all minor. I could list equally many negatives about LJ. The big reason I stopped using G+ is because of the nymwars. Google has started insisting that everything posted there be traceable back to your real physical identity, and (in order to make this enforceable) that the only people who can participate are those who have conventional Western-style first-last names. I find this unacceptable, repressive, totalitarian, and I don't want to contribute to it. I'm happy enough to participate under my own real name (despite a couple of incidents where acting as an admin on Wikipedia under my real name has led to people harrassing the real-life administrators at my workplace) but I feel strongly that there are many good reasons to be pseudonymous, that pseudonymity has been an important part of our culture, that disallowing it is also stifling free speech, and that it doesn't even work as a way of preventing trolls and spammers (because the trolls and spammers are happy to use real looking names).
Anyway, since Google doesn't make my posts there easy to search, and I'm not entirely happy about them being kept only on a service whose philosophy I disagree so strongly with, here's a brief timeline of my posts there.
7/10. The most obvious thing to do with my new Google+ account seemed to be to link it with some of my other existing online activity. I began with a cross-post of my LJ post on a James Turrell installation at the De Young Museum in San Francisco.
7/10. Cross-post of my LJ post on some of the accepted papers at FOCS.
7/11. Another thing I set out to do on my new Google+ account was to publicize some of the technical articles on Wikipedia that I'd been recently working on improving, among an audience I thought might find those articles interesting. I started with Theil–Sen estimator, a method from robust statistics for fitting lines to points in the plane. This set me on a pattern of posting much more often to G+ than I was posting to LJ, and of making much shorter posts with a few sentences of description followed by a link.
7/12. Implicit graph on Wikipedia.
7/13. Curtis–Hedlund–Lyndon theorem on Wikipedia, a topological characterization of cellular automata.
7/14. Video of St. Vincent covering Tom Waits' song Big Black Mariah.
7/15. De Bruijn–Erdős theorem on Wikipedia, about coloring infinite graphs, with a very helpful comment from set theorist Andres Caicedo.
7/17. Impact factor engineering (link to a blog post by Peter Cameron).
7/18. Crosspost of my LJ post on conference acceptance rates.
7/18. A plug for dermophoto's urban abstractions.
7/19. Crosspost of my LJ post on my county fair photos.
7/19. News story about Aaron Swartz' indictment for pirating academic papers (discussion).
7/19. Crosspost of my LJ post on nine new JGAA papers (and new material requirements for journal papers).
7/19. New arXiv preprint: Privacy-Enhanced Methods for Comparing Compressed DNA Sequences (discussion).
7/20. An expository video on the Steiner tree problem, with some discussion.
7/20. Factor-critical graph on Wikipedia. In the discussion, Jean-Marie Madiot makes the amusing observation that, because friendship graphs are factor-critical, killing any of your friends would allow all the survivors to form happy couples.
7/21. Hajós construction on Wikipedia, a way of automatically generating k-chromatic graphs. With some discussion about whether it can be made to generate all and only the k-critical graphs (probably not).
7/22. Graph drawing accepted papers.
7/22. Ear decomposition on Wikipedia.
7/25. A Wired story about photos of windblown sand patterns. I didn't say so in the post, but when I made it I was thinking about a similar photo that Jan Kratochvíl had included for my benefit in his SoCG 2011 talk.
7/25. The pseudonym problem first reaches my attention. With links to fandom lounge and geek feminism, and an image of pseudonym wank bingo from the geek feminism link.
7/26. Falsehoods Programmers Believe About Names, found in the context of a Google+ discussion on pseudanonymity and leading to a little more discussion.
7/26. Link to some 3d-printed jewelry leading to a discussion on artists who use 3d printing technology.
7/27. Link to some flat-origami tessellation patterns.
7/27. Link to another post on Google+ concerning integrating MathJax with Google+.
7/28. Reshare of a post by one of my contacts linking to a story on endemic plagiarism among computer security textbook writers. This is a case where I think Google+'s "circle" model is broken: the original Google+ post was set to "extended circles" meaning that only people within two steps of the original poster could see it. To respect that, I set my post to be visible only within my circles. But really, there's nothing in this that couldn't be public. So my choices were: strip off my contact's name and avoid giving proper credit for finding the link, fail to strip it off but make the post public, violating their privacy, or self-censor. I took the safe self-censorship route but now I'm not sure that was the right choice.
7/28. A brief description of the Kruppa–Demazure theorem (on reconstructing five-point scenes from two perspective views) in the context of a new Wikipedia article on Michel Demazure. Some time after that I got Demazure onto the front page of Wikipedia, briefly, in their "Do You Know?" section, with a sentence that included something about his pseudonymous participation in Bourbaki.
7/29. More on pseudonyms: a link to one of Skud's posts observing that even well-connected former Google people are having difficulty getting any level of non-robotic assistance getting their accounts straightened out after the banhammer comes down. In my post and the ensuing discussion I hinted that this issue might cause me to leave G+ but agreed to give the G+ administrators time to clarify their position.
7/31. Cross-post of my LJ post on toughness.
8/1. Apollonian network on Wikipedia. Leading to some discussion on how to find names of graph classes and some concepts closely related to Apollonian networks.
8/2. A video about the 120-cell, a four-dimensional regular polytope.
8/3. In an attempt to continue boosting the signal about pseudonyms, I linked to the My Name Is Me project and denise/rahaeli/synecdochic's explanation of why Dreamwidth deliberately allows pseudonyms.
8/4. Edge coloring on Wikipedia, with some commentary about how I find Wikipedia articles to edit.
8/7. Reshare of a post by Yaroslav Bulatov, including a link to Vi Hart's fun new video on spacefilling curves.
8/7. Link to Uli Westphal's mutatoes, a photo gallery of colorful and misshapen vegetables.
8/8. Link to Can't Decide? Undecide!, an article by Chaim Goodman-Strauss on undecidability.
8/8. The final straw: Google makes it clear that their no-pseudonym policy is firm. I link to a couple more pro-pseudonym pieces and declare a hiatus until pseudonymic people are treated as first class participants.