Good afternoon,
I went from 10.2 to 10.3.5 and finally to 10.3.9. The upgrade was flawless, and 10.3.9 has been VERY stable ever since. I do run Onyx about every 2 weeks and run Diskwarrior every 6-8 weeks. I have have never had an issue with any apps that I run, and my 15 year old son, well he's into gaming, chatting, and buying music, and he has yet to complain that there is a problem, and he has done several upgrades. I had thought about moving to 10.4 but plan to buy another iMac when 10.5 comes out, so I am staying with 10.3.9.
Hope this helps,
Johan