Afridi: don't write or fax to them yourself, but get your university to fax them a letter. You may have to draft it for them. When I spoke to my university, they said they will send the letter but that I should write it for them. Make it nice and official and try to get the Chair of your department to sign it.
Also, I went to Gerry's FedEx in Islamabad yesterday to ask them if they knew anything. They said the Embassy is running its own security checks on people and that's what's delaying things. I suspect something like that is going on for most people with delays.