Is there any rational reason I should want to own an Apple computer?
Perhaps, perhaps not...
I suggest you read the website and the comparisons...
Linux: 902
OS X: 800
Windows XP Pro: 691
Window XP Home: 665
Hey Im an OSS kinda guy. I am RHCE, and MCSE certified and I can tell you the best desktop OS bar none is OSX. Linux on my servers, OSX on my desktop..
Depends. The Mac mini can be a nice tiny Linux machine, for example. But yeah, if you enjoy building your own boxes and being able to completely customize them, then you're not really the target audience for a Mac.
If you're happy with LINUX and building your own boxes, there's really no reason at all to think about switching platforms. Computers are tools and you pick the tool that best fits your tasks. I'm an Apple user and believe that most tasks can be done exceptionally well by a Mac, but there are people out there who are unsuited to be a Mac user, and who work best with another operating system.
That said, you could try borrowing a Mac running the latest version of Mac OS X, and then recompiling your LINUX tools to run on it. Just for fun.