I run test searches about twice a month at different times a day. I test google, msn and yahoo. I run three different kinds of searches. In academia or information searches google seems to come out on top. For commercial searches msn almost always produces better and yahoo second. (I don't care what other people say about spam in there, I don't have a problem).
For service type searches yahoo seems to be better. For the past year both msn and yahoo have been more consistent, whereas google is never consistent.
I am happy with this. I would like to see the other engines to gain ground and we, as webmasters wouldn't have to tremble every time google burps.
I find the biggest cheerleaders for google usually run their ads. They don't want the hype to fall.
In my opinion google is the most capricious search engine to ever exist.