How long do I have to wait for my offer letter? It's been nearly two months (next week it'll be 2 months) since I got an email from the Doctoral School at a UK university telling me that I got the place and funding. After 4 weeks of waiting, I emailed them to ask when the letter would be sent out but they gave me no specific answer. Also by chance I learned that someone already received their letter nearly 4 weeks ago. I'm very worried and just wondering how long everyone had to wait to get their offer letters. And should I contact them again about it?
Pick up the telephone. Repeat several times to several people if first call does not get an answer.  

Get this resolved within a week.  Have them send the letter express mail.  No more sitting and pining.  If you haven't resolved it by week end, you need to move on and look for a different gig.