Skyguy9999 on 5/9/2010 11:10:31 PM:
On Mountain bikes, they're generally fine, I've found. The biggest issues with them, though, are the suspension (very hard to use, and unnecessary in most cases) and the added weight (because of durability to take it off-road).
If you consider touring beyond just a day where you need to carry things (water, food, clothes, and so on), you will want wider tires than the norm, because they will need to handle the weight you carry (your weight plus gear).
The bike store suggestion is great, they should be able to explain all the factors involved in selecting a bike and should help you be able to find something that fits well for you and will satisfy all the requirements you need.