I've got one. Great bike on the road, but very heavy when going off-road. One mistake and it's gone. Difficult to pick-up on your own on sandy ground. No problems with reliability (yet) when running daily (30000+ kms/year).
But i'll leave my TDM at home, and use my XT600Z...
Oh yes, do something about the seat. Having bum-problems after 1-2 hours on bike. (and windscreen, and...)
For more info start at:
http://www.carpe-tdm.net including some reports of people using this bike off-road.