Google is the stock that nobody wants to fail and in many cases embodies the tech sector as a whole. Sadly panic over a general market decline/perceived lack of stability in the U.S. economy as a whole has knocked quite a few strong stocks down a peg or two. Quite simply, GOOG fell because they ran short of projected earnings, people keep overlooking the fact that they are still growing and that they continue to deploy and improve products and still focus on acquiring technologies that they believe will influence the web not only now but over the next 6-18 months.
The price drop may continue, possibly even to $400-$500, but in general this stock will have to return close to it's previous $700+ levels. The pending Microsoft/Yahoo merger only emphasizes that the search field is paring down to a very small number of major players and Google is still clearly the winner.
I think the stock is overvalued and most likely will be so for quite some time, but based on market behaviour I think any investments made now will definitely realise returns within the next 6-12 months.