I still have my PowerBook G4. 15”, 1.67 GHz, 80 GB harddrive. Like a lot of others I currently use a MBP, but I still occasionally pull out the G4. It was a great machine, although it choked on HD playback, Flash, and RAW photos.
The only problem with it is the RAM. I only had 1 GB when it was my primary computer and one of those sticks has since died. 512 just isn’t enough these days!
Edit: I guess I should add I also have a PowerBook G3 (Pismo), although it wasn’t originally mine. 500 MHz, 256 MB RAM. Dual boots OS 9 and 10.4. I tried browsing the web using OS 9 and it’s not pleasant experience…