setzer - 7:27 am on May 20, 2011 (gmt 0)
I've noticed the way Google calculates site speed, it factors in external factors - like ads.
We have an extremely fast site that loads in < 2 seconds but the ads cause it to register 8-10 seconds in Site Speed. In real-world, this is really a non-issue for visitors since loading of the ads is in an iframe, so it doesn't interfere with bringing up the actual page. Shame that I'm getting knocked down in the SERPS for it (albeit very slightly) but oh well. There's nothing I can do about it.