I've got the J&G rain cape. And while it's well made, it's not long enough. You're constantly making sure it covers your hands, and doesn't fold up on itself at your butt. I'm gonna go with a waxed cotton one next time. I'm willing to spend the money to get something of nice quality and good function.
The principle of a rain cape is nice though. You stay relatively cool while riding with one, though you do look a bit odd.
-Gene-