Just thought I'd again add my support for both OSX and Linux versions of MC. I too think that the market for it could be larger than you might think, especially on OSX. True, there are a few mac-zealots that wouldn't use anything but iTunes (suckers), but also keep in mind...
A very large chunk of that small OSX user base are multimedia, sound, and graphic arts professionals, who could really use a powerful system like MC (and which otherwise doesn't exist for OSX).
However, that being said, I'm certainly aware that porting to OSX and Linux would be No Small Task
TM, considering that a sizable portion of MC's code depends on DirectShow and (now) Direct3D. I'm sure the effort would be only a few steps short of monumental.
However, it is also my suspicion that you guys put a very heavy focus on making sure your code is well encapsulated, and a lot of MC's architecture seems built on a plug-in object type system. This could, if it was done well (and I suspect it was) mean that it would be far easier to swap in OSX and/or Linux compatible components to replace the stuff built on proprietary Windows components, than it would be for most software vendors.
I guess that doesn't make it easy really... Just possible.
Here's hoping!
(Oh, and if you ever do, I'll certainly buy it and so would a hunk of my co-workers.)