I'll tell ya a little story, kinda humorus, about a buddy of mine. I'd been riding (again) for about 6 months or so. Was getting pretty good, riding Moonscape and Gatorback and stuff like that. Every Sunday I'd come home and the neighbor would come over and we'd talk and I'd tell him about the ride, ya know how it goes. So he decided he wanted to start riding. I said, "Great, head over to the bike shop and get a decent bike, a Walmart bike won't hold up to the stuff we ride." So the next week he tells me, "Hey man I got a bike, lets go ride this weekend!". Saturday morning he rolls over with a Walmart Mongoose. I just shook my head. It lasted about 8 miles. I wouldn't shift (at all), front and rear wheels were bent, rear brake didn't work, and the coup de grace was when both pedals snapped off simultaneously. It was kinda comical really, luckily he didn't get hurt. The next weekend we went to the LBS and got him a real bike.
I understand not everyone can drop a couple of grand on a bike. I ride a hardtail quite often, they aren't as comfy, but that makes you be a smarter rider. You'll learn to use your legs and body to cushion the bumps, pick better, smoother lines. Get the best bike you can afford. It'll last longer, and you usually won't have as many problems with it.