iMovie2 is more versatile and is easier-to-use. Among the differences: the Shelf holds as many clips as you want; the controls make a bit more sense; the Effects are more accessible; the Timeline is more sophisticated; slo-mo, fast-mo, reverse, brighten, and sharpen are now available; you can restore clips to their original form if you make an error; you can separate audio from video and manipulate them separately. There are more advantages, but these are the most notable ones. I have used all of these features and would probably pay for them if I hadn't already gotten iMovie2 built into my Cube. However, if iMovie has met your needs and you don't care about these particular features, I wouldn't worry about it.
You might want to go to an Apple retailer and try out iMovie2 directly - it's standard on all of the consumer machines. That would give you a better idea of whether it's worth the $ to you.
[ 08-10-2001: Message edited by: zigzag ]