Re: What bike did you build on...? CHIME IN
First of all decide what your going to do with the bike. Casual jaughts, show bike, commuting. Then decide on what style you like. Your skill level and budget will dictate where you go from there. The biggest draw back of the box store bikes is the poor quality especially of the components. If you plan on putting on the miles then buy quality everything. If you buy a cheap bike you will be upgrading hubs and wheels at the very least. after you pay for all the up graded parts you could have bought a quality bike except you still have a questionable frame. If your only going for a sunday putt once in awhile a box store bike might serve you well but I would still be suspicious of those wheel sets. With that said some members claim to have great luck with box store bikes and if it makes them happy who am I to fault them.
I don't know first hand but there are plenty of posts warning against aluminum frames due to cracking. In my opinion it seems like the best bang for the buck is a older high quality mountain bike with a sbp shift kit. All the parts are over the counter and minimal fuss and the frame and components are already heavy duty so over all cost would be minimal compared to some builds. I've seen Gary Fisher mointain bike on craigs list for $75 that was in great shape. Throw a few hundred bucks at sbp for a shift kit and expansion chamber and you have a solid bike that should haul butt.
If you get lured into more custom bikes like board track tributes or antique bikes kiss your wallet good buy especially if you have to have stuff made for you not to mention it's very trying if you don't have a knowledge or support system for antique bikes.