Family Guy also parodies these pretty well
I can honestly say I've never seen one of these products in real life. But people MUST be buying like crazy. These ads have been around forever, and if you "call right now" they throw a ton of product at you with free shipping for (what seems to be) a reasonable price. Clearly business is good.
So in order to curb my curiosity, if you have ever ordered from an infomercial, please post a comment here and let me know. If you live in the Chicago area, I might stop over to see the greenness of your grass/how well your vacuum works/how perfect your push-up is.