bikesaregood said:
You just compared mountain biking to bowling.
Well, you are throwing balls at things.........sorta.
I agree with the guy who said try local shops first. Unless you're experienced, and know what a half-degree head angle compared to top tube length, chainstay dimensions, pretty much everything, will do for your ride, you may wind up with a bike that's totally useless to you on the trails. Not saying you have to buy from the local shop, but I do suggest it. The majority will try to match price with cheaper chain stores, will set the bike up properly for you, make sure it's ready to ride out the door. Ask nice, and they may even swap out tires for a model that's better for you, and just charge you approximate price difference.
Otherwise, look at the material, components, stuff like that. Try to get as good as you can. Not sure if anybody is still building steel bikes, but if you're looking at two, same price, and same general parts, go steel. Cheap aluminum is a recipe for disaster. Heavier, sometimes, since the lower brands don't use taperwall tubing, too expensive.
I kinda like the feel of Gary Fishers, myself, they handle well. Fast, though.