Just to add a bit to this thread.... I am HUGE and ride a regular ol' bike. I wish I had gone ahead and bought a road bike when I bought my current bike, but was skittish of the drop bars and went with a hybrid. It is a "unisex" (read: mens) bike that I now realize needed a little adjustment to fit properly. It's not terrible as is, but could be better - but not ONE of the things that needs to be tweaked is because I'm heavy.

I am 5'10" and weigh in at 275 pounds. My bike has road tires and at first go I got a couple of pinch flats because I wasn't used to the way higher-pressure tires lose air so quickly. Once I learned to check my tires every time I ride, the problem vanished. I should probably consider getting my wheels trued, too - but that's more because my bike was used as a commuter on questionable pavement for a year and has been through a couple of moves. I do note that I keep my tires filled to the higher end of the manufacturer's recommended range because of the weight, and that when stopping I tend to allow a little longer stopping time than someone smaller might because of the rules physics - greater mass, greater inertia.

People will tell you all kinds of crazy things about being a heavier rider - that you need high spoke count wheels, special spokes, tandem hubs. Most if not all of it is a sales gimmick - don't be fooled!