In my experience, cheap bikes from discount stores almost always have fundamental problems with the frame, and every single thing on them from the headset to the bottom bracket are of the absolute cheapest make they can get. Most dangerous, I've actually seen the brakes simply snap off on relatively new Wal*Mart bikes when a kid tried to stop. The brake boss just snapped off the frame.

There's no upgrading that. I would do only required maintenance and save my money for a good used bike, or a proper bike from a bike store or elsewhere.

I actually got my road bike from BikesDirect - if you are reasonably comfortable with a wrench, it's a good option. I got what would be a $1500 road bike if bought locally for $800, and 4 years later I still love it. It's actually held up better than either of the bikes I bought from the LBS (one for more money).