I'm new to the road game but I can chime in about mtn. biking. I agree and disagree with some of the statements above. A mountain bike and road bike are 2 different tools used for entirely different jobs, and I think statements that one is better than the other are very short sighted. Personally, (thus far) I find my mtn. bike more comfortable but I'm in more of a freeride position. I run 2.1" tires at 40 psi on a steel frame with 120 mm of suspension travel and have not had a flat to date on the trail. This has more to do with maintenance and having good running gear rather than road vs. mtn. Plus when mtn. biking, you are out of the saddle every other minute or so, so this may help with the perception of comfort. Full suspension mtn. bikes have the susp. so the tires stay in contact with the ground and control is maintained; it doesn't have much to do with soaking up bumps for someone's sensitive bottom!

If I had to buy 1 bike, it would be a mtn. bike. A mtn. bike can get you down the road, albeit slower and heavier than a road bike. You won't win a road race on one. The first technical downhill rock garden on a road bike will leave it in a heap of twisted aluminum and shattered carbon fiber with tacoed rims. You won't win a XC or DH race on one.

But what fun is owning 1 bike anyway? I say everyone should own at least 4!