The Duqu Windows worm's zero-day exploit source has finally been found by MS to be a vulnerability in font parsing (which is done in kernel mode for some reason).
Although it probably doesn't really do anything adverse to most people, it's interesting to note that although the flaw is publicised by MS, they don't have a fix for it yet.
Affects all versions of Windows since NT4.

Maybe there'll be another worm out by then which exploits this flaw?