It really depends on how the charging is worked out. While I am opposed in principle to the internet being sold as a commodity like a kilo of apples, as a user who has BB largely for fast surfing and email, and occasional system patches/upgrades, with no p2p or gaming at all, I can't help thinking I'd be better off ...
I don't mind £25 a month for my 600k though; it's so much better than dial-up even just for surfing.
It might be acceptable if there was a light-user scheme a la BT for only the most occasional of users, taking the form of a monthly rebate for those who use less than a certain amount. Conversely, I would be happy to see high-user surcharges imposed on only the biggest bandwidth hogs. This way, we would avoid an all-out metered service but might curb the excesses of those who hog the network.
Alternatively there could be some kind of peak/off-peak scheme which would allow for the fact that very heavy bandwidth usage at 3am is far less intrusive on the surfing of others than it would be at, say, 7pm.
However it's implemented, it needs careful thought and planning by any ISP wanting to take this approach.
Which means we're screwed.