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According to WhatTheFont, which somebody just mentioned in the Web Design section, it's a lot like Memphis Bold, an Adobe font, which it seems you can get from that link for around $40.

It does look very similar, but if that is what it's based on, it's been adjusted slightly--the serifs at the top and bottom of the OSX font are sloped slightly toward the place where they connect with the body of the X, while it looks like they're flat horizontal in Memphis.

If you want it for a parody or something, just adding those slopes to Memphis should do it, though.
 
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