With Yahoo's similarly clean search results page, and reasonable useful answers, I ponder why I don't use it more often (especially since they are a bigger supported of Perl than Google).
But even if they returned identical results, with identical utility, I think I'd still be using Google nonetheless.
The reason is that it's really quick and easy to type "google searchterm", even with only 2-3 fingers, because it involves two fairly close clusters of keys.
In comparison Yahoo has keys in three locations, requiring either finger stretching or more hand movement. And capital Y has to be about the most difficult of all letters to hit.
While not as important in my opinion as the sparse homepage (which makes it a much better place to send my parents, or grandparents, and know they won't get lost) I do wonder if the need to stretch more to type reduces the attractiveness of the alternatives.