Really they launch very well. Yes they do spin the tire more than pretty much any other vehicle in the Universe(yes I being facetious). The older clutch driven models had more of a problem with traction than the newer automatic models(which also happen to have a reverse which is a godsend). The automatic models with the torque with the two speed auto are really very quick. Their topend is limited to about 150though so at the very top the rice bikes will end up beating them, it will just take them a while to catch up to do it. The newer models are coming with Avon 230 venoms on them which is a good grippy tire as opposed to the old Goodyear eagle tire which if not on a car pretty much sucks.
I'd love to ride one, or a Rocket III, but I can't see myself ever owning one. I just don't have room for more than one bike, and I need it to be a real all-arounder. My DL1000/V-Strom is reasonably comfy for cruising the slab, or around town, will carve corners something like a sport bike, and has the weather protection and luggage of a touring bike. Plus it has better than average dirt road abilities.
Up at the Friday the 13th rally in Port Dover (Ontario) last year I saw a Sportster set up as a dual-purpose bike, with high fenders and knobby tires. Interesting...