Calm down. This was purely a data error where old data was mixed in
with new. There were no unusual trades, even at the close. Take a look
at both highs and lows as well as the options and you'll see that it
was prevalent for all Google-related securities. It happens sometimes,
and there are rules in place to deal with it. All brokers and data
feeds sourcing from the Nasdaq will show this error, and any incorrect
ticker prices or trade prices will be corrected when the bad data is
removed.

Google is down a bit in after hours only because of people
misunderstanding the data-related drop. It will move back up as soon
as this fear goes away, and we will almost certainly see the mid-400s
tomorrow, much higher in a couple of weeks when they report (Google's
earnings have been stellar even through the economic downturn because
they actually benefit from slowdowns as resources are shifted to the
most efficient forms of marketing.)