The install for OS X Leopard went pretty smooth on both of my comprooders. The Finder enhancements are pretty nice tweaks, and the network drive handling is particularly better.
Time Machine is indeed every bit as cool as I thought, but it also expects you by default to do an all-or-nothing arrangement, which I'm not sure I really want to do. I've got the drive space, but it just seems like a bit of overkill. Then again, when you can buy giant drives for a hundred bucks, maybe it's the right thing to do.
You still can't backup by way of a network drive, which is a bummer, and .Mac is still pretty basic, unfortunately. Still, if you're not totally hung up on off-site backups the way I am, Time Machine is a drastic and idiot proof way to go. Well done.
I also upgraded iLife, because the support for AVCHD, my new camcorder's format, was included with iMovie. I've also wanted to do the new event-based organization of iPhoto, so it seemed like a worthy upgrade to me. Despite using the likes of Avid and Final Cut Pro, I have to say the ease of use on iMovie is pretty stunning. I plugged in the memory card from my camera and knew it was video. Ditto for inserting a data DVD of video I had the camera burn with its included burner. It just knew, sucked in the video, and worked.
Definitely a couple of worthy upgrades there, and I don't mind giving Apple more of my money when they deliver stuff that just works.