This is something I've discussed with my teams on a few occasions. Performing updates to applications usually ends up consisting of a hacky "down for maintenance, back in 10..." page put up by hand.
It's because nobody really thinks about it until the last minute. That's kind of as it should be, since there are usually more important things to worry about. I think the "back in a jiffy" pages are fine, but if you want something a little friendlier, that's where Wrenchmode fits in.