In the States, I've heard from users in NYC, Chicago, and San Francisco. They all report that Google searches were running at historically low speeds. I've heard similar reports from users Europe and Australia.
In addition, Google services like Google News and Gmail are completely failing. The Internet Storm Center is saying that it's received multiple "reports of a total fail of Google Applications. Gmail, Reader, Docs, News, Apps. etc."
The Storm Center also states that it has "Reports of Google working in some areas (West Coast, co.uk, and others), however the outage appears to pretty widespread for the most part. Probably depends on which Google Data Center you are connected to." I can confirm that users in the UK seem to be doing well.
The problem may not reside in Google's data-centers. In checking, I've found, thanks to Just Ping, that sites from around the world--at 11:45 AM Eastern these included Melbourne, Australia; Madrid, Spain; and New York Cit--were all seeing 50% or greater Internet packet loss.
I have also checked to see if Google's problems were masking an Internet NOC (network operating center) problem. That does not appear to be the case. According to the Internet Health Report, there's no significant overall network trouble among the major NOCs.
This leads me to conjecture that what's happening is a massive DDoS (Distributed Denial of Service) attack. Based on the size of the attack that would be needed to interfere with Google, I believe that it's quite likely to be the result of an attack from the controllers of the Windows worm, Conficker.
UPDATE: 1:38 PM, May 14, 2009. The Google services outage is not over yet. While Google appears to be better in most of North America. Google is still suffering serious network problems in the European Union and in South Africa.
Another theory that has been put about--that the problem was due to AT&T NOC routing problems--does not appear to hold water. Google outages were reported by users whose traceroutes showed that their connections never traveled on AT&T connections.
What are you seeing? Anyone know anything more? Let me know in the comments.
September 1, 2009 Update: Gmail hit by widespread outage