I took the leap about 5 years ago, i have a Powerbook G4, and while it has started to fail recently (some **** dropped it!!) its still functional. The faults i have are the Battery has died, but it can be replaced, and the usb's on the left side are somewhat troublesome but thats only a recent fault.
I have replaced it with a PC due to the fact i just couldn't justify paying for another mac, but the powerbook still lives as my websurfing machine. Over the years it has done everything i used to do on PC's and it one of those things that just works, the software works and the added hardware i have brought all works quickly and flawlessly, especially the software iphoto, garageband, imovie etc.. are great pieces of software.
On the negative, so this shows im not totally mac biased, non of my sony hardware works on my mac, i had a sony vaio mp3 player, this refuses point blank to work with my mac, was really annoyed with it, until i got my hands on an iphone!