#PitMad is the specific event I participated in, though it appears there are more. During this day-long event, you create a pitch (or multiple pitches) for your novel in 140 characters, post the pitch(es) up to twice every hour for the entire day, and some agents, editors, and publishers browse through the pitches and favorite ones that they would like to see a query for. If your pitch gets "favorited," that is an invite to send a query to that agent/editor.
So I decided to participate for the steampunk novel I am working on, just to give it a try. It was really fun--and also quite useful.
It was useful because it really made me think about the essence of my story. To sum up a 100,000-word story in 140 characters is no easy feat, and this exercise really helped me to try to boil it down to the essentials. What is the real meat of the story? What about it would grab a reader's attention? I'm still not sure if I came up with a good pitch (I decided to do it somewhat last minute, which I would never recommend), but I think it was still a worthwhile experiment.
Here is one of the pitches I came up with for my manuscript, Skylark: The Adventures of Captain Kay:
"Riots, explosions, pirates. Kit's had a rough week. But a stowaway with noble ideas to change the world could make it even rougher."
There is another Twitter pitch event coming up on June 18th, specifically for sci-fi/fantasy manuscripts, called #SFFPit. Here's some more info: http://dankoboldt.com/sffpit/
I think I'll participate in this one as well, but this time I'll plan in advance and see if I can discover more about what my story is really about. I'd recommend giving it a shot.