Re: [twitter] keeping in touch with others in my field of science
For myself, I can't see it as useful in any sense beyond the superficial. OK, so I suppose some of the shorter emails that I send might be twitterable. But 140 chars is way to short for me to have any kind of technical conversation, even given that a technical conversation is likely to include mathematics of some kind.
I can see how you might do PR for science via twitter, that would work well. But science PR isn't the science itself - even a one page press release on a result isn't science, so however apt the analogy you might use in your tweet (or pr) still isn't a fair representation. Which is not to say the twitterpr is worthless, just that it's a very distinct thing to the necessarily detailed science itself.
Science publishing might be broken to some extent, but I fail to see how any valid scientific article can be usefully replicated on twitter or social media - it seems to me that whatever the failings of journal-style articles, whether in traditional journals or not, twitter is not a replacement. It seems to me you have conflated the actual scientific content with the pr/publicity you would like to achieve for that content.
The conference thing is interesting. For myself, I just read/skim the timetable from the conference site and look up the authors or work independently. Twitter/hashtags might give a sense of 'buzz' around some particularly noteworthy result, which I guess might be helpful. But my projects tend to run over timescales that incline me to prefer to avoid obvious bandwagons and seek out still interesting but less trodden paths. I skim a much wider range of article/conference output than is ever likely to even microtrend on twitter.