This may be old news, I don't know, but Google seems to have taken away the commonly used words "feature". Try http://www.google.com/search?q=a+the+it

Before, it would have said something like: '"a", "the" and "it" are commonly used words and are therefore excluded from this search' (or words to that effect).

When did this happen?

I first heard about this just some days or weeks ago.