I was interested to hear about those beta usage gizmos, since that was going to be my next search, to see whether I could determine on the fly how much each action at the computer "costs" me in terms of capacity consumption.
The thing is, where I was able with dial-up to do a number of things that were essentially "free" (after paying the monthly fee to Orange), now they are not. Right now (8:40 on Wednesday morning) I've switched on a live steam to the Today programme. It saves me from having to disconnect my bedroom radio and move it into the computer room. But under dial-up I could listen to the BBC all day for "free". Okay, so the audio stream was sometimes interrupted, but it was a small price to pay in comnparison with now, under broadband.
Anyway, I can see that the ball, as ever, is more in BT's court rather than Zen's, so I'll start looking further into the way BT works out its wholesale charging, especially in comparison with other countries. For example, it seems from what I've read that the provision of broadband in France is far more advanced and greater value for money than in the UK, so this fundamental question may be something the government may be interested in.