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 in 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 question is 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?