you would need decentralized search algorithms. i haven't looked at that much myself, but there are some projects out there that seem interesting. to give an idea: when my friend is logged in, his browser could run algorithms that send me recommendations. think about how you receive information on twitter: not through centralized algorithms, it works through peer-to-peer retweeting. at least as a research topic, it is very interesting :) but you are right, there is stuff that's hard to do. i think the most challenging one would be google search.