I don't know how much you should take my response into consideration, because according to the Poll taken earlier, I'm one of the youngsta's on the board at a measely 35 years old. Most of my motorcycle experience in my life has been down and dirty on the trails of sand, rock, mud, logs, burms, jumps, etc...
I probably have a total of 100 miles of gravel road (I call 'em dirt roads) riding on my Burgman which has a total of 3000 miles on it. I think it does surprisingly well in the dirt. I have my springs set on 4 and have indeed have had self induced fish-tailing on the bike. (Hope my old english teacher isn't reading this.)
Ran into a big-o-patch of sand once at about 35 miles an hour with the scooter.
After doing an endo in the sand, as described above by Craig, some 25 years ago, I decided never to endo again. So after endoing in the sand another 40 or 50 times, I figured out how to get out of a situation like that.
Don't try this at home, I'm a trained nutcake; put all your weight on the extreme back of the bike, and gun it! It's all or nothing here. It would have probably been pretty funny to watch myself jump up off that big fat seat, land on the passengers foot rest and twist that throttle like there was no tomorrow. Of course, you must remember, that action also causes the bike to fish-tail, so you need to deal with that whilst trying to get out of the sand pit.

After fifty gabillion falls in my life, you start getting tired of falling, and start learning about "Steering Geometry". All bikes have a self correcting design to compensate for any lean at any speed (Except slow) and remain standing straight up, moving in a straight line. It'll do that with OR without you on the bike. (This is where all the engineers jump in and tell me I'm wrong, there's way more to it than that... and there is, but that's it in a nutshell) If you can figure out how to always stay on your bike, and not let go, and have enough room to go straight forwards, you'll always come out fine if you're not going too slow. We normally wind up in trouble because there's not enough space to go straight forwards... Usually a guard rail, or sign, or building, or automobile, or boulder, or that stupid 8 inch tree branch we won't talk about. :shock:
Of course a 550 pound Burgman is not the bike to learn this type of stuff on. I started riding a 80cc dirt bike many eons ago. I think those bikes weigh 150 pounds give or take, and you can throw these bikes around like a paper plane and can literally beat 'em to pulp, and they'll still keep running. (Ahhh, what fun that used to be!)
But back to the question at hand... I think the Burgman does absolutely fine on maintained dirt roads. You might not want to take it down the road if it looks seriously degraded, and/or freshly grated. Newly grated roads are fun to drive on ONLY if ya like to fishtail a lot. Go around bumps, and keep your speed down. (This paragraph is one of those, "Do as I say, not as I do." type of things.) And by all means,
if you don't feel comfortable in any way, shape, or form, turn around, it's not worth getting hurt, dying, or worse... Scratching your Scooter!
I have yet to bottom out the bike, I do go around the big holes, don't drive that fast, I don't drive as crazy as you probably think I do, and as much as I've wanted to, I have kept the scooter off the trails.
Always ride safe!!