I have a hard tail MTB, love it and ride it everywhere. That's my problem though, I have to ride it everywhere. I love riding on the road, and even though I've fitted my bike with semi-slick tires, and tried shaving weight off eevry way I can, it still doesn't feel as light and fast on the road as my friends road bike.
Like most people, I bought a MTB because I had pictures off tearing down off road paths and thought the sturdier construction was great. Then I began riding on the roads with a friend and found out how sluggish it is on pavement. About that time I found cyclocross bikes, and was amazed there was such a bike as this. It looks like a road bike, but has thicker tubing and wider, knobby tires to take the punishment from off road. What I love about them though is the fact that you can put slick tires on them and you've got a pretty decent road bike. You won't be winning any road races or breaking new speed records, but it's a hell of a lot faster than a MTB on the road, and as far as I can tell, just as good on the trails I use my MTB on.
I've got half the money I need to buy the one I want. Just need to save the next half. I am accepting donations.