Someone posted this awhile ago, too. If you want to use the round-key U-lock, a trick they suggested (maybe it's one of these posters) that sounded quite viable was oiling the key hole. Poster said that makes it impossible for a Bic pen to get any purchase in the hole. If this actually works, seems like it'd save you a lot more money...
I figure if someone's taking a dremel or saw to my back wheel, they've rendered my beater fairly worthless, as that's the only part of my crap-ass bike that's worth more than 20 bucks.