What I like about the idea is the fact that you could "walk around" finding things you wouldn't imagine searching for conventionally, but still get the benefit(price?) or buying online. But whatever you find in there you would still want compare to "the real Internet" i.e Google, price comparison sites, which makes it an unnecessary layer.

Also how are businesses going to showcase their products? SL and OpenSim is not really great for masses of text and pictures, and these are people who run webshops. I worry a mall would look more like this:
http://fsvo.rymdraket.net/slbtc.jpg