sheldon's lock strategy is sketchy. don't use it unless you really have to.

the "different tools" theory is crap: it depends on the locks, the tools, and the motivation of the thief. you may stop a thief, you may not... it WILL take longer to cut through two locks than one lock, so to that extent it is a deterrent... but if the bad guy has a van, and only one lock is securing your bike to a solid object, the 2nd lock can be dealt with at the bad guy's leisure.

note that the video posted earlier in the thread, with police and TV stings, all of the bad guys had very small tools suited for cutting cheap/crap cables. ask the campus police what tools/techniques are used to break locks... or what types of locks are most often busted... if U-locks and heavy chains keep the bike safe, use a U-lock and/or a heavy chain. if the bad guys are using angle-grinders, then your best defense is a cheap/ugly bike.