Revolving Door Villains

There’s a running joke that in high-magic fantasy games, death is naught but a revolving door and the party cleric is the doorman. I haven’t played much 4e myself, but I’ve heard many of the epic-level abilities start out “Once per day, when you die…” If there’s a bigger way to hang the “death doesn’t matter” out for everyone to see, I haven’t found it yet.
What about villains, though? Unless everyone is playing a pulp-style adventure, having the villain inexplicably escape every time he’s encountered can seem contrived and simple GM-fiat, but can the revolving door be used as a plot device to present the players with a unique challenge?
There’s also the issue of the omnipotent adversary. Inexperienced gamemasters can fall into the trap of giving their adversaries full knowledge of the party’s actions even if said adversary lacked a sufficient means to gain such information (by spying, scrying, etc). But again you can run into the trap of the cookie-cutter with things like the traditional wizard with a crystal ball.