Blogging is a great format (https://web.archive.org/web/20120611100409/http://blogs.plos.org/mfenner/2009/10/01/conference_blogging_interview_with_alex_knoll/?) to report from conferences. The regular blog format works best for posts written at the end of the day – unless you are typing really fast. Microblogging, i.e. a number of short or very short posts by a group of people, works better for live blogging of an event and has become very popular.
FriendFeed (https://web.archive.org/web/20120611100409/http://www.friendfeed.com/?) was probably the first widely used microblogging tool for scientific conferences starting in 2008, and a January 2009 paper (https://web.archive.org/web/20120611100409/http://dx.doi.org/10.1371/journal.pcbi.1000263?) describes the experience at 2008 ISMB conference in Toronto. By late 2009 Twitter had surpassed FriendFeed in popularity, and at some point in 2010 most people seemed to have switched from FriendFeed to Twitter for conference microblogging.
Twitter is a great tool in many ways, but is far from perfect for conferences. The biggest problem is that the tweets about a particular topic aren’t really connected. Hashtags help to find tweets about a particular conference, but hashtags for a particular session have never cought on. This makes it very difficult to have a real discussion, or to find related messages later on.
Facebook is not only extremely popular, but has also taken many of the features of FriendFeed. But for some reason it has not become a popular conference microblogging tool for scientists. I think this is because many people use Facebook primarily for their social interactions, and keep those separate from their professional discussions.
Google+ (https://web.archive.org/web/20120611100409/http://plus.google.com/?) was released last week, and the services has many of the features of FriendFeed and Facebook (who bought FriendFeed in August 2009, one of the reasons the service has never become that popular). Google+ allows discussions around a particular message (post, tweet?). It doesn’t have groups about a particular topic (e.g. conference), and doesn’t yet understand a concept similar to hashtags. The service looks very nice from a desktop computer, but the mobile version for iPhone and iPad isn’t very polished (I haven’t tested the Android app).
The experience from Twitter tells me that the most important feature for a great conference microblogging tool is popularity, and this is only partly related to the technology behind the service. There are already a good number of science bloggers and other Science 2.0 folks on Google+ and we have seen some good discussions (e.g. a discussion about conference microblogging (https://web.archive.org/web/20120611100409/https://plus.google.com/106537123721037364937/posts/buxDWrvq8vU#106537123721037364937/posts/buxDWrvq8vU?)), so that is a very good sign. But the experience with Google Wave (discontinued (https://web.archive.org/web/20120611100409/http://blogs.plos.org/mfenner/2010/08/09/what_comes_after_google_wave/?)) and Google Buzz (not that many people seem to use it) makes me a bit cautious, and I will wait how Google+ evolves in the coming months before I get too exited.
Update: Added a paragraph about Facebook.