Make sure it is really an 03 (serial number, way the monocoque looks). I came across some guys selling 00 or 01's as 03!
Check if it is one of the late 03 models with replaceable derailleur hanger, otherwise you are screwed when you crash because new chainstays are not available anymore. If the frame has it not I would ask the seller for a huge discount.
Other than that if it hasn't been abused the 03's should be fine. Earlier models had problems with headtube cracking if you were a heavy rider.
Shocks are kind of an issue as well if you plan on replacing them. Only 5th and Swingers (pre-07 style) fit, as well as Romic and shocks with remote piggyback.
Further there are just a few replacement parts on ebay floating around, so if you plan on racing that bike it can be quite a hassle to trace down those parts in the middle of the season. If there weren't the replacement part issues this would still be one of my first choices as a race bike. M3s should be the faster bike though.
