At first I was livid about these new tariffs (as my post in another thread testifies), but now that I've calmed down at this 'backwards step', I think I am in fact going to upgrade to iPhone 4 on O2 (I specifically skipped the 3GS so I could get the true upgrade), and lose my unlimited data.
For me it was more about the psychological impact of suddenly getting less for my money, the idea of having a limit in general, and having to worry about huge fees if I go over on occasion (my average use is about 400mb). I feel like that's the case for quite a lot of people. And you probably use less data than you think. And if 3% of people really account for 36% of the data traffic, we probably will see a marked improvement on the speeds we're getting at the moment.
If it's indeed only a £5 fee for up to an extra 500mb if you go over your limit (I can't really figure out if you need to get that as a bolt-on or if it's also an automatic charge as the Financial Times was saying), then that's not really a huge deal for me.
Yes O2 are greedy b*stards, who should be doing more to improve their infrastructure, and who should be offering 1gb as the base plan for that money (which would surely also cut out the extremely heavy users), but it's not so bad. I also think that the deals on the new iPhone across all networks are going to be very similar. It's an industry shift, and there are already data caps on several networks.
This whole thing isn't as big a deal as first appears.
(or maybe I just want an iPhone 4 and am trying to convince myself...

)