I use a PowerBook G3 Wallstreet (released in September 1998) as my primary system still. I got it at the end of 2001, and was running Rhapsody 5.6 (Mac OS X Server 1.2) on it until the released of Mac OS X v10.2 in August of 2002. I am still running 10.2.8 on it today. I upgraded it to 512 MB of memory shortly after I got it, and then upgraded it from it's original G3 (at 266 MHz) to a G4 at 500 MHz early in 2003. In late 2003 I replaced the original CD-ROM drive with a CDRW, and when the battery finally died in 2004, I added a second 20 GB hard drive to the system in the second expansion bay (it has a 40 GB drive as it's primary).
So, I've been using this system or a little over six years, and because there are things I just like better about 10.2 when it comes to writing, I'll most likely still be using this system for years to come.