On mine I've changed:
Brakes: New levers (Deore front & SD7 rear), Inspired pads on rear, Carbon booster on rear (There is a lot of flex otherwise)
Pedals: Echo TR's (Original ones seemed to prefer gripping to my shin bone rather than the soles of my shoes)
Chain: Trialtech K710 Kool (As said before, the original chain looked snap happy)
Grips: Unbranded lock on's (Original's wore through after a few months)
Bashring: Czar (Managed to squish/ snap part of the original one... Im a bit of a basher)
Forks: Palshey (Original's are relatively heavy)
Freewheel: Echo SL
Although that makes it look as if I've changed loads, its mainly been due to them coming up cheap on here rather than there being anything particularly wrong with them
I've used it mainly for 'trialsy' type riding with the odd bit of street and seems to cope with both perfectly for my level of use, has been loaaaads more fun than my old Mod and iv'e improved a lot more in a short period of time in comparison, so well worth it in my opinion