Facebook servers presently are not able to handle the load of their 500+ million users and have been out for a while now.
Facebook’s Status page gives few more details –
Latency issues resolved
Sep 22, 2010 5:08pm
The API latency issues we were experiencing this morning have been resolved. Sorry for the inconvenience.
API latency issues
Sep 22, 2010 1:40pm
We are currently experiencing decreased latency across the site (including Platform APIs) due to an issue with a third-party networking provider. We are in contact with this provider and working to resolve the issue as soon as possible