[ljf]

Yes, I've used them many time, and I know my (non technical) girlfriend does too.

I've found similar novels that I've liked through the suggestions, bands I've enjoyed and recently when buying the 'Lean Startup' I ended up buying 2 of the suggested books.

Many time I end up not buying the item I originally went there for, instead buying one of the suggestions, or the suggestions on a suggestion... depends how the reviews look.

As I see it Amazon were the first to really use this data successfully and meaningfully.

The other networks I guess would be the Amazon Wishlists which for a time were hugely popular. I still see wishlist links on personal and informational sites, as a way to give back to the site creator. That network is pretty powerful too!