Twitter hashtags for professional activities

Hashtags are a great way of labeling or tagging twitter posts (aka "tweets") for searching and compiling by others. For more info on hashtags, see hashtags.org. They are commonly used by members of some groups for identifying group-related activities (e.g. amateur radio operators often tag their ham related tweets #hamr) or to label events (e.g. the recent wildfire in Boulder, CO prompted tweets tagged #boulderfire). People can then search for occurrences of these hashtags and identify others who are tweeting about a topic or group of interest, and they can save these tweets if need be.

Recently I post to Classroom 2.0 and the Science Education Research ning and proposed using a specific hashtag for science education related tweets: #scied. I've also been using the hashtags #AERA and #NARST to talk about the upcoming respective conferences of the American Educational Research Association and the National Association for Research in Science Teaching. My hope is that we, as a community of educational researchers and science educators, can start to use these and other relevant hashtags in order to facilitate searching and compiling of tweets for community-building and even research purposes. 

The twittersphere is collecting a huge number of new tweets every minute- that is a lot of information to keep track of, much of it very useful but only if we can find it. What hashtags do you use with respect to your professional activities? What others should we be using?