Google went down sometime around 3pm (EST) for many people. I know it was down for me in New York and if you look at tweets around that time for [google down] you will see hundreds of people saying the same thing.
See that spike? Spikes like that do not lie.
Here are some tweets from people reporting Google was down and then up and then down:
Forum discussion at Google Web Search Help.
Update: A day later, Google admitted they were down. Google's Rubie said, "yesterday around 12:00 PST, a small percentage of users had intermittent access to Google that lasted about 20 minutes."