I just upgraded this afternoon. The install process knocked my laptop out of commission for a full hour, but it worked exactly as advertised. I haven't run across any compatibility issues, however, because I tend to do server-type work in a VM. Things seem about the same with a bit more visual/timing polish and "solid" feel.
Did you buy the box set or the leopard upgrade? I've heard the upgrade will work as a full-install for tiger users.
I used the $29 upgrade from Leopard - not sure whether it would function as a full installer.
It does work, but it violates the EULA (and is practically piracy), if that sort of stuff matters to you.
It's great that it works as a stand-alone install too - I was hoping it would. I'm running Leopard now, but I'd like to do a clean full install of SL.
Most Tiger users are probably on PPC, a CPU that is not supported by Snow Leopard. And please remember that Windows XP has a huge botnet problem.