This topic came up in a recently recorded Brainstorm Podcast episode - Do you use BBEGs and if so, how do you go about designing them?
For me, I rarely go into a campaign with a BBEG fleshed out, let alone thought out. I always figure my players will designate some NPC their nemesis and I'll go from there, but then again, my parties are like herds of cats, you never know where they are going to go.
Then again, I've played in some campaigns that have very effectively utilized BBEGs, so maybe it's a deficit in my DMing skills that leads to the leaving out of bBEGs in my games.
So, where do you stand with BBEGs? Yay or nay? Power behind the throne or in the face power manipulator?