Nothing produces Twitter followers faster than tweetcasting an interesting event. Once your followers figure out what you're doing (you should tell them beforehand) then they realize that the next several minutes or hours are going to be a "target-rich environment" for pithy quotes. And so they start re-tweeting you to all their followers, many of whom just might follow you as a result.
This assumes, of course, that the people speaking at the event are saying pithy things, or that you can distill what they're saying into pithy things. If they're terminally boring, then you should be somewhere else anyway. But most speakers consider it their duty to the audience to bring their best (and most quotable) material to a presentation. So you're likely in a good place.
It’s hard to tweetcast your own presentations, but you can easily tweetcast others in your panel. Matter of fact, it’s really entertaining to tweetcast other panelists, as they’ll often say something about it while you’re doing it. If other panelists mention my tweetcasting, members of the physical audience start following me as well.
If you're on a panel, then you'll almost certainly be tweetcasting from your smartphone or tablet. But if you're in the audience, try to find wifi and an electrical outlet because you can get several times more quotes if you're tweetcasting from your laptop.
Three final note on tweetcasts…
(1) there's no doubt you'll annoy a few people, some of whom will even unfollow you, as a result of your tweetcasts. But you'll get far more followers as a result. And you'll also get a number of highly appreciative emails from people who could not be at the event, but are really happy that you are, and that you were covering it for them.
(2) A tweetcast is a great way of saving your notes from the event to the cloud where they'll hopefully be there until the end of Twitter… and hopefully you can scarf them just before the end.
(3) Go back as soon as the event is over and favorite ("fave") the best quotes so you can find them easily later. Also, if you're keeping a database of quotes, copy the best ones there as well.