As of Mountain Lion, Preview has been "upgraded" with a ridiculous font choice for its Notes (Control-Command-N). I use them all the time in PDF files and suffer from the Comic Sans feeling of Marker Felt.
Is it possible to change the font used by Preview to show notes?
It does not seem that the question has already been asked.
Best Answer
Sadly, it is not possible to change the font used by Preview for Notes - this is denoted by Apple an 'UnEditable'.
This thread on the Apple forums (which I can't take credit for) provides a couple of work arounds such as using Annotations instead of notes (as these are editable) or post-editing comments in Adobe Acrobat Reader XI, but not an actual solution to this problem.