I don't actively seek revenge because I feel it's wasteful, but I will accept it. Or rather, if something bad or some form of poetic (or relevant) justice happens to someone who wronged me, there's the possibility that I'll take some degree of joy in it. It really depends on the nature of what happened.
When my ex-girlfriend called me one night after the guy she left me for broke her heart, the only thing on my mind was making sure she was okay and cheering her up. She was a good person and didn't really wrong me, she just made a choice that wound up hurting me. Prior to the actual call, I felt lot of spite over what happened, but that totally changed the moment I heard how much pain she was actually in. She didn't deserve it. I do draw lines.
On the other hand, one of my best friends recently got a new girlfriend, and suddenly has eyes only for her. He won't even stop swooning over her like some kid that's never touched a woman before long enough to help out one of his friends (me) who's in a potentially dangerous situation. If she dumps him and he winds up without any real friends to turn to because he kept blowing them off and ignoring them when they needed him, I will relish it like a fine, fine wine.