I don't care what people say, if you have your laptop on for a few days, it's going to lag.
Haven't you heard of sleep mode? I can't remember the last time i started up.
Nope, I'd rather cut off my right hand than go back to 10.4
<3 Leopard
UI animations aren't as smooth, it's true.
But I haven't had any application stability problems with Leopard (CS3 is not crashing for me, at least any more than it did under Tiger) and giving up Spaces and Time Machine at this point would be like cutting off my left hand. I'll stick with Leopard, thanks.
Do you have enough RAM? Leopard is definitely more RAM-hungry than Tiger. 2GB on my older MacBook Pro (sadly, it won't accept more) is just barely enough. 4GB on my Penryn MBP is quite comfortable.
Tiger felt more robust to me. But I could never go back because I use Spaces all the time.
One issue that is really getting on my nerves with Leopard though is if I minimise a window to the Dock and then put the computer to sleep, when I wake it up again the minimised window cannot be maximised again, and I have to force quit the program.
10.5.2 is substantial improvement for me over 10.4.9. Time Machine alone is worth the upgrade.It was until i was playing around with 'Mainstage' that comes with Logic that id had enough. the cpu usage during mainstage was always about 25% even when doing nothing and it would often peak when i never remember there being any problem before. There was also a noticeable lag after pressing the key which i never had before.