Some interesting stuff about how iPlayer has affected viewing figures (short answer: not as much as you'd think):
The iPlayer's an amazing invention, but the majority of television is still watched live. Something like 89% of television is watched live. If you get 200,000 on iPlayer - which is still a lot and can add to the overnight - it's a relatively minor amount overall. Particularly for mainstream... It's different for Being Human, which got about a million on the overnight and then we added about 500,000 through repeats and iPlayer.
I think Skins and Shameless actually get more from their non-original Tx, although some of that is still linear repeats. But mainstream television certainly is, contrary to popular belief, still very much watched at 9 o'clock on the day it transmits. Catch up obviously is increasing, but if you get three million for a show on BBC1 at 9 o'clock, you're not suddenly going to find that you actually reach 6 million. And the pick up on iPlayer for Five Days is no more than it is for anything else, which I was quite surprised by. I thought it'd be way up.
We got six and a half million for Five Days, ten million for Doctor Who, sixteen million for EastEnders. ITV got nine million for Unforgiven. Mass audiences still want to watch TV live. They still want to find something as it happens, they still want to feel that sense of liveness and freshness. I'm sure it will continue to diversify and the figures will continue to get smaller but audiences still want to turn on.
Full Ben Stephenson interview