Hi
I am having similar problem on iPhone as I am on iPad.
iphone 4 3.3.3
ipad 2 3.3.3
I have latest ipadi/iphone software 4.3.3, 50mb virgin connection, D-Link DIR-855 802.11n Quadband Router. no problem streaming with 4od or my home pc in high quality with vlc streamer.
With iplayer app I randomly cant load content and then when it does load I have major streaming issues (keeps stopping and sometimes reloads to begining)
Very frustrating.
Does not seem to be any support coming from BBC or Apple on this????
Anyone found a solution yet?