Live-tweeting (see also live-blogging): Broadcasting messages on twitter in directly relation to and following the goings-on of the event you're currently participating in .
Livetweeting also has the ability to be a kind of note taking. If you've ever watched a live blog, it's the same concept, just with a shorter text field.
If you haven't and have no idea of the concept, here's a recent one:
http://live.cnet.com/Event/Googles_next_dimension_of_Maps_ev...
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Tweeting: Wow this conference is boring as heck, and the food sucks too #firstworldproblems
Live-tweeting: Foonly just announced that the foomatic v2 will have high-speed backchannel integration! #foocon2012
This is not twitter-bashing, I really feel that as a matter of basic decency and for their own intellectual growth audiences should be actively listening and making connections so that after the talk they can have something more interesting to say than "tl;dr".
If you are so caught up in your initial reactions to a speaker that you pre-emptively distract yourself you are missing out on a lot of opportunities for insight into yourself and your community. I don't see the value in dozens of people flying to a city just to sit in hotel ballrooms and regurgitate things over the wifi.
Because of the fleetingness of the things we do online, even if the particulars are boring and mind-numbing (e.g., reading fifteen Cracked Top 10 articles in a row, or fruitlessly tweeting to tech celebrities in hope of a reply), we don't notice because the experience in general gives us the impression of fulfillment by virtue of its variety alone.