Google is the so called king of search. More than 200 millions searches are made using the Google powerful engine. People trust it more than you can imagine. Most of them don't even think about using any other engine like Yahoo or Live.
How good is Google? Good question. I personally never liked Google very much because of the way they rank the pages. They use the so called Page Rank algorithm that ranks better pages with a lot of links specially from "important" pages. Of course such system is easily manipulated like you can see many times that you search and you are pointed to farm website that contain nothing but ads.
Now let's see Yahoo. I always liked this engine because it shows relevant information all the time and their Rank System seems not to be easily manipulated. I never found a farm page using Yahoo. The results they show are always relevant to the keywords you type. The only problem is the layout. Google layout is better and lighter than Yahoo.
If you want the most accurate results, use Yahoo.
This makes me think why the worst browser in the world is still the most used web browser. As you know I am talking about Internet Explorer. The best, fastest, most secure browser of all time, Opera, is the least used browser! How is this possible? Are people ignorant? Maybe.
I encourage you to try Yahoo and Opera and see the difference in your searching experience.
(I will give yahoo some credit for having the automatic search completion thing, that was handy, but that\'s also included in the google toolbar for firefox)