When I hear things like this it drives me crazy. For 3 years (99-2002) I worked at an Apple dealer and did Mac repairs (friend owned the store, I had a photo studio in the back), I am an experienced Apple Tech. Obviously the experience that Saltcured had is not indicative of something wrong with Leopard, but rather something seriously wrong with his machine and/or HDD.
If I had to speculate as to a single issue it would be his hard drive. My advice would be to back up all the 'created by user' files and erase the drive and reinstall everything.
Unless the HDD is about to die this should save it. The only reason I'm suggesting an erasure here is that he has already installed Leopard, probably over an already corrupt system that was heavily fragged. This way, his machine, his HDD, gets a new lease on life.
I just had to do that with my wife's MacBook Pro. She thought her SuperDrive was broken, it wouldn't eject, it wouldn't mount, just did not want to work (This issue existed for the past 3 months). I wound up having to hook up an external burner, reinstalled Tiger (which fixed everything including her SuperDrive. Then installed Leopard, afterward did a PRAM fix (anyone that does Archive and Install should always to a PRAM reset afterward to blow out any garbage that collects). Once her Spotlight indexed the machine ran MUCH better than before.
Since 9AM yesterday morning (when my copy of Leopard arrived) I've helped 26 friends, family, and co-workers (we're a company stocked with Macs) install and/or upgrade to Leopard with NO negatives showing up. I swear Leopard will go down as one of the most "complete" and "bugs-kept-to-an-absolute-minimum" .0 releases.
Simply put, in Saltcured case, Leopard is NOT the problem.
Sorry for such a long post from a newbie. I've lurked for years, but had to address this because its such a diametrically opposed reality to tens of thousands of other Leopard users I've been reading about and in those that I have assisted today, er, I mean yesterday. (long day!)
Bummer is I've only been playing with Leopard for 30 minutes and I've already had several issues. System preferences has crashed several times; mail can't write to my keychain, I have to enter my email passwords each time I restart mail; frontrow can't access my iPhoto library, gives an error message. I hope 10.5.1 comes out soon.