We did something similar over time. I started with my Mac Mini switching from Linux as my primary, then my wife got sick of her XP desktop and we went all Mac.
Well, not really. Her old XP box sits next to me as I type this, but it's off and rarely gets turned on. The last thing I used it for was to convert some Garmin maps for a beta of their MapCreate software for Mac (they call it "Bobcat" I guess to keep with Apples 'big cat' themes for their OSes) which for some reason you needed to have a Windows XP PC to do the conversion of the 'unlocked' maps for their software.
Oh, and I suppose one could say that this other XP PC I have on the other side of my desk....nah, it has a TV card in it and that's pretty much all it functions as. I use it pretty much exclusively as a TV hooked to my DirecTivo and standalone DVD recorder. Kind of like if you've ever seen a crashed automated teller machine you'll see that it's running a version of OS/2, or a point-of-sale cash register that is windows based os-wise, but otherwise is a one-trick pony.
Okay, I also have a Parallels VM on my Macbook that is Windows XP SP2. But I only boot that up when I need to show people I can do it, and also to get recordings off my wife's voice recorder, which is not Mac compatible.
Other than that, it's all Mac all (99.999999999%) of the time.
BTW for those that may have purchased Parallels to run the odd Windows-only thing on your Mac and you got it back when it was a version 2.X, then had them release the much improved 3.X version, they have a program where if you can prove that you purchased it at some time-frame you can upgrade to their latest version for free if you go through some hoops. I went through those hoops and just got my download and unlock code for their latest version today. So now my only "XP PC" that I ever really use (which is once again, on my Macbook) is now at the latest revision. For free!