I love mine, its a sand tank, there are few easy mods for the DS, Carb mods, and either a End cap or good exhaust and they run great, they do need help with the A arms- for handling ASR sells special Upper A arms and FireBall racing sells great a arms for the DS which really helps in the handling overall on the DS.
Engine is pretty much bullet proof with normal maintenance, the hot set up is Ron Wood A1  cams, ported intake and the HSR45 Carb, End Cap or RW exhaust system, electric start is nice too!
You have 3 great builders for the DS 650 , Ron Woods Racing http://rotax.net/   The Bom (Jeff Ross) http://www.thebomracing.com/  OMW Racing (Mr. Horsepower) http://www.omwracing.com/