First up, I will admit to being a bike snob. I have no issues with that.
As far as the Retail Store bikes go, I think that you can get something that will be ridable, but you need to be careful in what you buy.
If you buy a full suspension bike (I won't call it an MTB) for $150 (or even less), then you are asking for trouble.
But if you spend that same sort of money on something which is fully rigid, then you should be getting something better. All of that suspension adds cost, so if you get a bike with it, then they must have cut corners elsewhere. Further, go and ask a bike shop how much it will cost for them to put the bike together, it is often about the same as the price of the bike. From speaking to Bike Mechanics, these bikes often use proprietary parts, which means that when something does break, you can't replace it.
Although some people may use them as a stepping stone to get into cycling, I sometimes fear that they do more harm than good as they are often heavy and can be unreliable. No doubt if they are put together properly, then you may get a decent life out of them. Typically, whenever someone asks me for bike advice, the first thing I tell them is to go to a bike shop, yes you will spend more, but you will get a bike that the shop will stand behind.
Also, someone sent this to me a few years ago, this is the other side of the Huffy Bike, how are they made so cheaply?
http://www.nlcnet.org/campaigns/archive ... sdoc.shtml
And finally, a story, I was talking to a mechanic about Huffy's, and he told me that when he was at school, someone there got a dual suspension, he was jumping it down a flight of stairs. This came to a halt, when after a landing, he didn't just buckle a wheel, or snap a pedal or something. No, he snapped the frame! I think that this supports the "Do Not Ride Off Road" sticker.
James