There have been a lot of revisions since '01. The biggies are:
-Frame changes in '03 and '05 - the '05 handles much better than anything you've ridden
-Marzocchi TiN coated front forks in '04 ('03 in EU)
-New engine cases in '05 - dropped some weight and addressed the crappy ignition cover
-Dual mapped CDI in '06 (some '05s had the CDI, but no switch)
-Porting, crank bearings, pistons, reed cages and etc. have also see changes over the years