ive known a few guys with them,, even rode one around a bit on a nice mixed trail. they were/are very expensive,,, just saw one for sale used, asking price is 16k i think?
having ridden one, and a GS and a ktm 950 i can honestly say that the HP2 is a blast to ride with a pretty light feel and great suspension, however the width of the jugs limit you to where you can actually use that suspension. if your thing is riding similar terrain a GS can but faster/more aggressively its worth it, otherwise get a gs800 or ktm950.
edit; just like to clarify, its a totally different bike to ride than a GS, my thoughts are that it just wasnt the competition to the ktm950 bmw maybe hoped for and they are addressing that with the 800,,, i dunno.