I love Time Machine because...
...I don't have to think about backups.
Usually hard disk failures and accidentally deleted data happen without thinking. I only start thinking when something that's important to me is no longer there. Time Machine just chugs away in the background, backing up my stuff every hour.
...it's so efficient.
I'm not even aware that it's running unless I happen to glance up at the menu bar at the exact moment it's pushing out a change to my backup and the little clock is spinning for a few seconds. My system doesn't slow to a crawl, I'm not swapping disks, nothing. Backups just happen. It happened while I was typing this post!
...it's got a seriously cool restore interface.
Yeah, Okay, I'm a sucker for cool UIs. Time Machine has one of the coolest UIs I've seen when it comes to restoring files. The animation is first rate and it's not just eye candy; when I needed to get to a version of a file that I had made dramatic changes to I could roll back in hourly increments to the point I needed very, very quickly.
...I have a feeling it's going to save my ass.
I have always been horrible about backing up my personal data at home. At work it's easy - large scale shared systems that backup important data all the time. But there's always an IT guy at the office that worries about that stuff. At home, I'm the IT guy and backups are one of the things I hate thinking about.
If you have Leopard but are not using a backup system, start using Time Machine right now! Go out and get a cheap USB based hard drive (you can get a tiny 320GB WD Passport drive for $200), plug it in, reformat it to a single Mac OS Extended (Journaled) partition and then point Time Machine at it.
If nothing else setting up an "always on" backup system will ensure the data gods look on you with favor and don't wreak havoc on your hard drive.
That reminds me - I better trigger my Windows backup!