Target and Walmart bikes are good if you are like the average consumer who buys a bike, rides it for a couple days and then leaves it in the garage or sitting out in the yard for the rest of it's life. If you actually plan to ride a lot then you need a bike from a LBS. (local bike shop)

There are plenty of good bike shop bikes gathering dust in garages. So if you don't plan to ride much, go with the Target bikes. When comparing prices between X-mart and bike shops, keep this in mind: If you spend $150 on a bike at Target, it is basically worth ZERO when you walk out the door with it. Try and resell it a year later and you won't get squat for it.

Good bike shop bikes like Trek, and Cannondale etc. will hold there value pretty well. It is not uncommon to see 1 yr old bikes on Ebay selling for more than they were sold for originally in a bike shop.