I now have Cubase and Logic and.....
I recently purchased Cubase SX 3 for my pc. All I can say for those who are looking is that Cubase for the PC is very stable. On the mac it is not! Logic on the Mac is very stable, Logic on the PC version 5.5.1 doesn't work well on XP. Had a chance to mess with Sonar 5 at a friends, and I no doubt will stay with Cubase on the PC.
I don't really get the Mixer and all of it's options in Cubase SX and it's much easier to use the mixer in Logic. It makes more sense using Logics Mixer. Cubase sounds really good, Logic sounds incredible. The plugins with cubase, should be a commercial for Native instruments, like "buy us, you'll need something!".
It really boils down to platform preference. I am going to be recording some more intense projects with Cubase soon, so we'll see. On a Intel p4 3 ghz it's very stable, and I get about as much polyphony as I do on my G5 running Logic 7.1. Also, cubase doesn't use as much startup memory as the other programs like Sonar and Logic(pc), so I suspect that's whats making the polyphony count higher and track count lovely.
Anyways, my thoughts for those who are thinking about switching from one to another, in these days of Apple uncertainty.