"Even then, once I have trained the search engine on my profile, what will I have gained other than teaching some other aggregator about the things I like?" I

"Even then, once I have trained the search engine on my profile, what will I have gained other than teaching some other aggregator about the things I like?" I guess that's the real answer. People are more likely to switch if they have a problem with the search engine they currently use vs. something "better" coming along. "Better" in search relevance is super subjective as well.