You know, I had a start-up idea along these lines recently: something that would combine SRS with social bookmarking.

Example: I'm slowly-but-steadily working my way through Learn You a Haskell for Great Good. I have it on good authority that few people make it as far as I have. I feel like the only reason I can do it is because I stop to make cards for terms, concepts, and many of the examples. I take days or weeks away from the book between sessions while I let those facts firm up in my head, and then I resume.

While I hold that there is real value to making cards yourself when this involves putting things into your own words, making a high-quality card is also a time-consuming chore that is just as much about formatting. I've often wished, as I read, that I had a browser extension that would let me pluck pre-made cards out of a side-bar that went with the passage I was reading -- cards by one of the thousands of people that have no doubt come before me in that chapter.

You can see how this might work. People could build karma when others copy their cards. Site creators might create their own cards as a way to help readers and boost traffic, or pay bounties of some kind to others who make them.

You could browse other cards by the writers of cards you've cloned, and all cards would have automatic links to the sites they go with -- getting around a big problem with imported cards, which is that they are shorn from their creation context.

Monetization? Maybe ads in the corner of the side-bar or something. Maybe partnerships with popular for-pay learning sites.

There are no doubt some thorny copyright issues at play though, and the overall potential market is probably pretty small.