My brother is an engineer and bought a Walmart bike. No problems. I got a cheap KHS Urban X for $329, but even that was a big bite for me. For awhile I was in love with a Breezer for $750 or so, and it was nice, but not TWICE as nice. Don't back down from bike materialists, especially if you are not riding for prize money. Example: I'm getting my 6-year old a 20" upgrade from her 16" beginner bike. Am I goind to plunk down $250 for a nice kid's bike when a $50 at Target will get her down the road just fine and is just as purple*? I don't think so. Of course if you become a hardcore rider you may want to upgrade, but I'd burn that bridge when you cross it, y'know? I'd be more concerned with Walmart's union-busting policies, but that's another rant... Get yer cheap bike and get the wind in your face. That's what it's about.
*my daughter's main requirement