Well, technically, it's not as big a jump as say, Linux-to-Windows (or preferably the other way around ), but still, even I'd love to get a Mac since OS X is essentially all the goodness of a UNIX system, but with enough commercial support that I won't be left in the dark!
The issues I've encountered have been mainly related to Unix tools that aren't included in OS X, but that's mostly being addressed by macports and homebrew. Though there are still some kinks here and there that kind of frustrate me as a developer (I'm just so used to the awesome package managers built in on *nix systems), it's been mostly smooth sailing from GNU/Linux land to BSDish Mac.
Linux to Windows..oh my. I can't see myself doing that.
Well, I had to make the Linux/Windows transition because a lot of the games I have don't work very well under Wine (sound drops out a lot, and running anything Source engine-based on anything but Low graphics settings results in a DX8-related crash), but all in all, I'd still rather use Linux over Windows.
Closest I ever got to really using OS X on my computer was in Virtualbox, and even then it ran so slow it was pretty much unusable for any practical purposes. From a technical standpoint though, yes, the closest thing you're probably going to get to a package manager under OS X would be Macports (App Store is one in name only IMO since it's essentially just a glorified version of whatever's on the iOS devices), and I couldn't even get that working in my virtual install since I didn't have XCode.
Oh man. Yeah, emulating games under Wine is pretty bad on Linux. I had some Steam games, which would run fine, but were ridiculously slow. I had some graphics problems as well (might have been my old laptop's crappy graphics card, though).
I tried running OS X on vbox as well, and it was also slow/unusable. Ever try hackintoshing? It can be a pain as well, but it's mostly usable if your hardware is supported.
The App Store really is a glorified version of the store on iOS apps, haha.
I've heard that my current desktop (a Dell XPS 410) is great for Hackintoshing, but I've never been one for suffering through all the pain of making sure all your stuff works and/or doesn't burn your house down under OS X. If I want to use a *NIX that's guaranteed to work with my hardware, I'll stick to something like Ubuntu. (Unless Apple would be generous enough to throw a bone to non-Apple PC users... or something gets rolling with Darwin, anyway; it is open-source after all and I wouldn't mind seeing someone make an Ubuntu-like system out of it.)