I've not updated to iLife '11 as yet. I'm waiting to see if I'll go ahead and take the plunge to buy a new MBP to replace my MBook (May, 2007).
What's interesting to me is that any time I work in iMovie ('09), it seems the processor goes batty on me. Sounds like a lawn mower. I usually only have a couple of tabs on the go at the time, iTunes is open, Pages, maybe Evom and Skype. Not using them, just open.
Anyway, IMoive must be quite the pig for processor usage, huh? It'll crash periodically, too. Nothing lost. Just a pain to re-open.
Any advice, thoughts, expertise to share?
/M.

No info on what Mac OS, RAM or available HD you have which doesn't help for a possible solution.

Try quitting ALL apps, and restart and then just have iMovie running, and maybe have a look at your Activity Monitor (Utility) to see what else your Mac is doing.