enigma1 - 2:31 pm on Mar 1, 2012 (gmt 0)

First of all make sure you do not have any DNS problems with your server. The next part I would check is the mysql. You could rule it out by uploading some basic html and see if it takes long time to load.

Also the google webmaster tools will show what googlebot reports as average load times, latency spikes etc. If the report shows your site is fast you may want to check your javascripts or other external resources that are pulled in.