i installed leopard, lived with it for 2 or 3 weeks, and then reverted to tiger. I don't think leopard is ready for prime time as of 10.5.1.
stacks is a broken mess.
the new dock UI changes are non-functional. (the blue fuzzy orb?!?)
despite what everyone claims, when i reinstalled tiger, everything felt faster.
networking is currently a huge pain in leopard
lots of the "cool" features have too many stipulations: intel-only or more RAM than any mac ships with, HFS+ formatted drives (not particularly useful for people who need to interact with windows and move things on external hard drives)
weird glitches all over the place
a new Finder that's barely any better than the old, horribly broken one.
no wireless Time Machine
Front Row won't keep playing when you navigate around the interface
"Smart" (stupid) dock icons break all the UI rules apple helped develop for no reason or benefit
So I could keep going, but I'll stop. Basically, Leopard isn't ready the same way Vista wasn't ready when it was released. And honestly, the same way Tiger wasn't ready at 10.4.0
But Tiger got a LOT better by 10.4.1
I thought Leopard would do the same, but literally none of my concerns were addressed with the update.