We have our own crawl/index/serve technology end-to-end. We have a 3 billion page web crawl, a machine-learning trained ranker, and then the slashtag vertical features. Since BOSS gives us an additional 20-40B pages for very long tail queries, we fall into /yahoo if we don't have any of our own results.

We're auto-firing slashtags for certain regular queries now, e.g. [cure for headaches] will auto-fire /health, [industrial design colleges] will auto-fire /colleges. We're doing this initially for health, lyrics, colleges, autos, hotels, recipes, and personal finance.

Getting the crap from sites like ehow out of the results and pushing results into a curated set of high-quality sites for queries in spammy categories really cleans up the results there.