Here's a list of what I've done to mine, happy with everything so far.
Mods:
Powder Pro's
2 Cool Side Vents
Amp Offset Riser (for Sno Pro bars)
Amp Gauge Cage
Skinz Super-Q Can
Tether
RotoPax Gas Can
Slide Kicks Ice Scratchers
FrogzSkin Mid Hood Vents
BDX Anti-Stab kit (HIGHLY RECOMMENDED, search Track Stab)
Free Mods:
Cut Windshield
Cut Snowflap
Remove Foam
Remove hood vent metal screen
Move ski's to skinniest stance (if primarily riding powder)
Remove Mid Boggies (the ones under the rear shock, search Bent Rails)
Things to Check:
Clutch Alignment (use 1.507 bar)
Belt Deflection
Track Tension/Alignment
Ski Alignment
Diamond Drive Bearing (I still haven't done this, search Diamond Drive Bearing Failure)