From what I've heard, there are only two real downsides to owning a Duc. Your maintenance intervals for the valve adjustments suck. If you drop it and break something, it takes forever to get parts. Reliability is above reproach, it's just like ragdoll said. Take care of it, it will take care of you.
As for the maintanance intervals... My 748 valve adjustments are every 6000 miles. I think that is reasonable eventhough it is a little expensive. If you drop it. Find someone that can weld plastic and replace the broken parts on ebay. After I dropped mine at Jennings Jet was able to locate the left clip on, clutch lever, and foot peg on ebay. I think he paid $25-$30 for everything. I just sent the plastics to a guy who can fill in the big hole in my left fairing and repaint it. A lot cheaper than replacing the fairing and front cowl. Things are expensive, but like anything else there are ways around it.