I tried Google's co-op search tool couple weeks ago. Unless you're a non-profit it'll display ad words. It allows you to create your own search engine experience customizing the web sites to be included on your search, refining labels, and other settings.
This morning I was thinking that it's a pain to have to manually maintain the list of websites that should be including, most likely a growing list over time.
Then, I was thinking that if you consider your included websites as the core of your search and you follow outgoing links you will highly probably find the list of your extended neighborhood where your search should be targeting.
Right now when you setup your co-op search engine you select between two preferences:
"How to search included sites:
. Search the entire web but emphasize included sites.
. Search only included sites."
There could be a third option that would be, "Search the entire web but emphasize included sites and proximity sites". The definition of proximity sites would be those sites that have less outgoing link distance to the included sites (the included sites have 0 distance, the sites linked from the included files have one degree of distance, the ones that those ones link to have a two degrees of distance and so forth).
This way the search would give the most relevance to the included sites (increased page rank), then some extra relevance to the sites in greater proximity to the included sites (some page rank increase depending on degree of proximity) and lastly it’ll be bringing search relevant unrelated sites (standard Google page rank).
It does reduce the maintenance time, as if I forget to include newly linked sites into my included sites, it will happen automatically for me as soon as I include a link on any of my included sites to a new one and exponentially through the new of proximity links.
Another alternative would be to offer this option to the end user when they do the search. (search: co-op name, co-op name proximity, web search), this way you could define a Google search for your website without having to set any set of included sites but just looking at the site you include the link itself and automatically calculating the closer neighborhood.
Actually this search is opposite to the 'Similar pages' link that appears in the regular search, so another option would be from the search result page to have 'Neighborhood pages'.
I know outgoing links have had no relevance whatsoever in the current search scheme, but I think that changes when you're site centered as opposed to web centered.
Anyway ... just a thought ...