I ran a sanity test just to make sure there wasn’t a problem with the agent: http://www.webpagetest.org/result/111004_G7_ff7ccb5350ffc3b90381af52bfe53457/
The only guesses I have are:
1 - some form of server DOS protection that is holding down the connections from the SF agent
2 - some really screwy routing between the SF agent and your server (though I’d expect that to show up in the socket connect time)
3 - a problem with the test agent that only manifests itself on your site
I grabbed a packet capture to get a better idea of what is going on: http://www.webpagetest.org/result/111004_6A_c9edcb6f78e4b9f598a2c3f570bb4db8/
It looks like the server ACK’d the actual HTTP request and then 20 seconds later the response started coming so from a network perspective it looks fine (but slow).
If you don’t already have it turned on, you can add the server response time to your access log and then tail the access log with a grep filter for PTST which will only show requests from WebPagetest. That way you can at least tell if it is somewhere in the application or in front of it.