I got Time Machine set up on Friday. It does not seem to slow my system down and keeping a FireWire 400 External Drive attached to my Intel-Mac workstation, all the time, does not appear to make my system buggy, like it did with my old Sawtooth G4.
After my entire workstation was backed up a few times, I launched the Time Machine app and was visually blown away by what I saw.
Speaking of my old 400 MHz Sawtooth G4, I pulled it out of the grave yard in my basement and inserted an old 7200 RPM 80MB drive that had a clean install of Leopard (installed through my Dual G4 back up server), and I added some extra RAM, pulled from our old decommissioned G3 iMac.
This old G4 works pretty good with the unsupported install of Leopard. It's old 2002 Radeon 8500 retail graphics card, with 64 MBs of DDR RAM, helps it to perform OK with Leopard along with having 1.5 GBs of RAM. It has enough horse power to allow my son to play some of the web-based games on the Lego web site. Aaron has "Pack The Man" and "Snood" on the old Sawtooth and they both work fine. Some of the iLife '09 and iWork '09 apps work fine as well. So my 1999 G4 is now my 9 year old son's computer. He is playing on a system that is older than himself.