I just want to throw in another vote against the cheap department store mountain bikes... and for a used bike.

In my area, most bikes I see are the type that you asked about. They are usually being ridden very slowly on flats and down hills or pushed up hills.

The hills they are being pushed up are the hills that I ride up without too much trouble, and I weigh over 300 pounds.

So the bottom line is if you want to ride the bike on the road, don't worry about getting a bike that pretends to be able to ride through the wooded mountainside... get one that is meant for the type of riding you will do, and it will serve the purpose much better.

Even if the full suspension mountain bike was entry level quality for real off road riding, you should know that the energy absorbed by the suspension is sometimes YOUR energy, and therefore means that less energy is used to move you forward. They are also heavy... A double detriment for road riding... Less efficiency and more weight.