Tonight I had the unfortunate - but fortunate - opportunity to take full advantage of Time Machine, so I thought I'd share my story. I'm happy to say that it worked great (except for a couple of minor fluky things)! After upgrading to 10.5.3, I restarted my computer. Something must have gotten corrupted, because it wouldn't restart. It would get hung up on the grey screen, fans would kick into high gear for a while, and then it would just turn off. Not good. I grabbed my install disc and was able to boot off of that. But I was getting a file system error when I tried to verify the disc. Right before I went ahead with attempting to reinstall OS X, I saw a menu option to restore from Time Machine. I forgot it had this capability - I tend to think of it for just restoring individual files. I haven't really heard of anyone using it for this but figured I'd give it a shot. Very cool how it works - You can chose which backup you want to use for your restore. And it shows you what version of OS X each backup uses. So I was able to go back and select the last 10.5.2 backup. After almost 5 hours, the restore completed. Everything is there, and the system appears to be okay! Phew - I have to say, Time Machine worked great! This one issue made the Leopard upgrade worth every penny (and then some)!