Here is a list of websites that has something to do with 'social bookmarking' or 'search based on human indexing'.
- feedme links
... and here is a great resource for understanding the players.
Now, I can surely see the value of this approach -- automatic indexing based on links and keywords is very limiting and it is believable that human-indexing can improve the search results.
However, at the same time, here are the problems:
- There are too many pages on the web. Human indexing can cover only a miniscule portion of the available web pages
- People who understand and willing to contribute to the index (by bookmarking and sharing them) are the long-tail, geeks.
- As a result, this approach only seems to work with subjects that would be interesting to techies and geeks.
- It's hard to expect people to just sit and bookmark random, generic web pages, and newer, more interesting pages tend to get bookmarked.
So, as a result, digg is one of the most popular, successful sites. I'd like to see a website with a business model that can attract my mother to use and bookmark all the pages she knows. Now, that's what google should be worried about.