I use Time Machine, but intend to use SuperDuper as well once the Leopard compatibility issues are solved. (It's taking a long time, but that appears to be because the SuperDuper author is a really careful guy. That's what you want in a backup vendor.)

For Linux I just use rsync. Restoring a failed Linux system often requires fiddling with Knoppix as well; get a nice recent Knoppix disc burned and ready to go in an emergency.

Don't forget: have more than one backup, and have an offsite backup.

I never really tested my Windows system backup solutions; I decided to abandon Windows instead. For backing up Windows files I used to use SyncBack: http://www.2brightsparks.com/downloads.html -- it was pretty good.

I need to work on doing better online backups. A lot of my work is web stuff, though, and that lives on other servers anyway.

I too used SuperDuper! with Tiger but as soon as I got my hands on Leopard, I started using TM. Why? Well, it's automatic. Problem with SD! is that I would forget to plug my external HD sometimes and the backup would not go through. You can enable to backup TM to a HD attached to AirportExtreme (with a small hack) so that's my makeshift TimeCapsule and works well because I don't have to remember to do anything.