There are so many things going on in Google Labs that sometimes you can find yourself stumbling upon an interesting creation from them that you had missed. I discovered Google N-Grams while reading a post in Alexis Madrigal's blog in The Atlantic.
NGrams searches the occurrences of a word (or a comma delimited list of words) in Google Books from the year 1800 to the present and plots their frequency on a graph. You can start playing with it here: http://ngrams.googlelabs.com/
Here is a sample experiment to get you started: type "selfish,selfless" into the search box, click search, and then view the results.