I started with one of those in April of 2008. I was under 300 lbs and kept breaking spokes. I had the wheels replaced with hand-built wheels which solved that problem. I replaced the horribly saddle with a Brooks. I eventually swapped out the handlebars for a straight bar with bar-ends. The rear derailleur was crap.

After over 3000 miles, the bottom bracket shell cracked. As it's part of the frame, that was the end of the bike for me.

Don't get me wrong. I paid $225 new at a bike shop, and that bike got me back in shape. With new wheels it could do the same for you. Why not buy a bike with better wheels to begin with though?