The Grauniad had very similar problems...
From where I'm sitting, guardian.co.uk was painfully slow, with pages taking five minutes to load and often loading only partially, resulting in a jumbled mess. Ditto for Facebook.
It appears to have been a routing/DNS problem, and something to do with caching servers e.g. akamai.net.
Observing my browser status bar, I noticed that things ground to a halt as the browser tried to connect to static.ak.fbcdn.net. A quick search brought up a fix, it was suggested to use a ping/traceroute service such as ping.eu to obtain the offending server's IP addy, and include it in the machine's hosts file. This turned out to indeed solve 99% of the problem.
Same fix worked for the Grauniad, with the problem servers being static.guim.co.uk and combo.guim.co.uk.
I have to admit I was slightly flabbergasted, since I use opendns which is usually quite bulletproof.