Improvising makes me gulp; I get a visceral reaction before I go on stage. To be honest, this is a reaction I have to lots of similar situations: concerts where I was a soloist while back at school, plays, presenting, teaching. It's part of why I do it, although it doesn't feel like that at the time: adrenaline starts to rush through my body, and I want to throw up. But that passes, quickly, and then I'm on a high. I could probably sit down and rank the different things I do according to how great I feel doing them, and afterwards. Improvisation, and teaching improvisation, would come out at the top.
For the last few Barcamps I've been to I've taught impro for half an hour to whoever turns up; Barcamp Brighton 3, last weekend, was no exception. Best of all, we had a big enough crowd to play one of my favourite games to wrap up. I know it as The King Game, from Keith Johnstone (p237 of the Faber & Faber edition of Impro for Storytellers, if you have it), and it's particularly satisfying because you end up with a huge mound of bodies on the stage, all of whom are still paying attention to the scene.
Basically, people come in as servants, and the King orders them to commit suicide when (as inevitably happens) they get irritated. It's actually very hard to be a good servant, but some people actually try very hard to be bad (and in a quick session, it's generally more satisfying to play like this, admittedly breaking all the rules of good impro). Where it gets interesting is where people come up with strategies to avoid being ordered to die; at the weekend, someone came on as the King's daughter. (I think she actually lasted less time than the average.) The only time I've ever seen someone come on and survive was when I was doing this in Cambridge, preparing for a Whose Line Is It Anyway-style late-night show, and one of the women walked on and seduced the King. I suspect that works quite well as a strategy in real life, as well.
I've actually done much more of teaching improvisation than performing over the last couple of years (something I hope to change); but it does at least provide a (weak) segue to Seedcamp, where I'm a technical mentor this year. Looking over the entire list of mentors is a little daunting, but there are enough people on the list that I know from various things to make me feel I'll fit in. If you're one of this year's 22 finalists, I'll see you on Wednesday 17th, talking about How to Scale. According to Tom Coates, it has something to do with elephants.