This is a little silly when you consider volume. A search engine should crawl millions of pages and sites, and over time develop quality indicators so the crap can be filtered out. Anything that works equivalently to Google's algorithm will suffer from the same crap infection as Google results, and to a lesser degree any of the other top 20 engines and meta-search tools.
Something like ublock lists and p2p sharing in closed communities could provide semantic indexing and gradual manual curation, so with a few thousand people you might get novelty + quality in an engine. If you stick to a small, curated list of sites, you won't get site level novelty, and quality will eventually suffer relative to searches that scan over new things.
Even then, consider reddit - build a reddit search that's as good as Google. That updates once an hour.
Sharing bookmarks isn't feasible when you want the functionality of a general purpose search engine.
Something like ublock lists and p2p sharing in closed communities could provide semantic indexing and gradual manual curation, so with a few thousand people you might get novelty + quality in an engine. If you stick to a small, curated list of sites, you won't get site level novelty, and quality will eventually suffer relative to searches that scan over new things.
Even then, consider reddit - build a reddit search that's as good as Google. That updates once an hour.
Sharing bookmarks isn't feasible when you want the functionality of a general purpose search engine.