Until this point, I have demanded that my players not build characters with evil alignments, as I am familiar with how to design campaigns and adventures around "good" or "redemption" themes.  However, my players are both interested and drawn to playing darker themes and characters.  I would like to try my hand at an evil campaign but really have no idea where to start.  So my questions are this, what are the essential features of a successful "evil" campaign?  

I'm interested in both mechanics to accurately reflect the downside of being evil (playing a 3.5 or PFR system) and general advice/features to consider.  If you could provide concrete examples from reference material (movies or books), that would also be appreciated.

As a corollary, is there a way to prevent the evil campaign from becoming so distasteful (horrific, misogynistic, etc) that I can't bear to continue to it?