http://www.thedifferenceisobvious.com/
Microsoft were trying to sell Visual Studio 2005 "Spot the Difference", but I guess you can ignore the Visual Studio thing and play the game.
UserAgent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.8.0.4) Gecko/20060508 Firefox/1.5.0.4
