I've never bothered to install iPlayer, I just watch things live. Here at work we have a gert big link from Janet to the Beeb (I think they peer at LINX), so there's never any speed issues, and at home with my 8M Zen connection I don't seem to have any problems either (although Zen have been working with the Beeb in the past using multicast for video, so maybe they have some nice big pipes between the two).