The kernel's VM performance is poor, and its networking stack is flaky. There's a race condition or something like that which Azureus, a popular bittorrent client, happened to tweak when opening a lot of connections, hence the kernel panics that plagued azureus users for the last several releases. This, of course, should be impossible. But, the kernel is still immature, and hasn't had the benefit of years of tuning the way the mainstream server kernels have.
Of course NFS is separate from the kernel... my point was, OS X is not ready for primetime. And, Pengu, just because you "played with" the NFS server does not mean it works the way it should.
OS X will serve files. I never said it wouldn't. It just probably won't be as reliable or as fast as a true server OS. It very likely will be easier to administer, though, as long as you're not doing anything too far off of the beaten path, so if ease of use is a high priority, then OS X will fill the bill. All this is irrelevant to the original discussion of whether the Mac Mini is an appropriate server.
You can run a web server out of a matchbox, but that doesn't mean you should. I think you (plural) may be letting your Mac zealotry get in the way of reality here. I use my mac every day as my primary work machine, but that doesn't blind me to the benefits of other hardware and software platforms in certain situations.
