If you search on google for “photos of snow”:

http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=photos+of+snow

My website has a hit on the first page. But, google indicates that the “of” is a common word and is not included in the search. But, if you then search for “photos snow”:

http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=photos+snow

The results are different and my site doesn’t show up in the top results.

Therefore, contrary to what Google says, these “common” words are significant in searches.