In an entry last month I suggested that iMovie 3 was so slow that only those with the fastest Macs rely on it for working with multi-clip projects (and those without such zippy Macs use the far-sprightlier iMovie 2 for the lion's share of their editing).
I recently completed my latest Breen's Bungalow in iMovie 4 and I regret to report that this advice applies equally to the version of iMovie included with iLife '04. Unlike iPhoto 4, which is noticeably more responsive than its predecessor, the latest revision of iMovie is as sluggish as ever. As projects get bigger, one sees the Spinning Beach Ball of Death ever more frequently as the program churns and churns away over actions as simple as shifting an audio clip or using the new direct trimming feature (a feature which, except for these slowdowns, is welcome).
Note, however, that given the increasing complexity of my videos (the latest includes multiple audio tracks and loads of transitions), I may have outgrown iMovie -- I could be asking it to do more than it was intended to do (or do gracefully, at least). As brilliant as I find its interface, it's probably time to trade up to Final Cut Express.
Updated to add: Reader M. Clark was concerned that my observations might be based on a bad attitude toward Apple rather than iMovie's performance -- particularly since I didn't mention the specifications of the Mac I was working with. Those specifications are:
Power Mac G4 933MHz,"," 120GB 7200 RPM hard drive,"," 1.25 GB RAM,"," Mac OS X 10.3.2
The movie in question contains a mix of 60 still and motion clips and around 30 audio clips.
It's worth noting that iMovie 2 is far more responsive with this movie.
Another reader suggested that fixing permissions helped improve iMovie performance on his Mac. I fixed permissions as well as ran OS X's cron tasks with Cocktail and noticed no improvement.
Those interested in the experiences of others might care to peruse "," exchange on Apple's Discussion forums.