It's a great in betweener for imovie and final cut pro price wise although it is much closer to final cut pro as far as difficulty goes. It has most of the features that FCP has and is a great way to learn it without droppin 1000 bucks for FCS2. Look at the tutorials on the apple website and you'll be good to go.
Love Final Cut Express, and have used Final Cut Pro. Unless you really are a "Pro" there really is no need for it. There really isn't much of a huge difference between Express and Pro. Final Cut Express is a lot easier and faster to use then iMovie once you get the hang of it. Oh and if you haven't seen or used it yet, the new iMovie is AWFUL! It's more like iPhoto then anything else. If you plan on making videos and want them to look good, I would either buy or DL Final Cut Express. This is coming from experience with using the old iMovie, the new iMovie, Final Cut Express and Pro.