I changed to Post Office today. Everything went smoothly and the installation of the Post Office broadband was a doddle. With AOL my speeds were typically 0.2-0.3 Mbps from 3pm onwards, making iplayer, youtube etc impossible.
Now I am getting 5.6Mbps all the time
AOL are charging me about £66 for breaking the contract early (it was due to run to April 2011).