How can I speed up iMovie?
I think I've fixed my problem. I had 1000+ movies in iPhoto, and since iMovie just treats them as 1 huge "event" it was trying to open an event with 1000+ movies in it. My HD only had ~10GB empty. I exported them all out of iPhoto, moved them to an external HD, separated them out into individual folders and imported each folder 1 by 1 as a separate event, keeping the files stored on my external HD. I've now got my 3 years of video files all imported and have created 3 different projects which I've taken to completion and posted to Youtube. iMovie is lithe and snappy once again!

So, tips for speeding up iMovie:


Free up HD space so you have >10~15% free
Make sure your events don't have too many video files in them (anything over 50 is getting close to the upper limit it seems)
Consider an external HD, preferably SSD (You can use multiple drives to hold your "events". You're not just limited to your primary HD)