Why do you have to "switch" search engines as if they were insurance companies or something? It's not like Google has a frequent searcher program! It takes one second to search Yahoo if you don't like Google's results for a query.
Sure there's no hurdles to "switching", but most people I know (myself included) only use one search engine, and it's been Google for many years now.
I remember back in the day using multiple search engines (like with Dogpile), but then Google came along and it was good enough to replace everything else and I never looked back.
With lifehacker declaring "Score one, Microsoft" for Live Search's
Cashback program over Google Product Search, and Yahoo! search opening up to developers, I don't recall Google's supremacy being challenged this much in a while. The Yahoo! platform in particular is very exciting.