I was a member of this club but quit last year when I realized all I was doing was paying an extra $5 a month that was essentially subsidizing those who used MUCH more data than I did. In the 4+ years that I have had an iPhone I have only once exceeded 1GB, and that was only 1.2GB. Usually I use less than .5GB. And I do occasionally tether (MyWi and now iTether for my 4S). But I am usually near wifi so rarely need to tether. I also fear little from AT&T because I have not heard a single report about AT&T cracking down on tethering when on a metered data plan (indeed I don't think they want to traverse that slippery slope). In fact AT&T has gone the other way: the tethering add-on used to only get you the benefit of tethering. Now you pay $20 more per month but you are also getting twice as much data--a much better deal IMO.
So in the last 15 months I have saved $75. Not much, I know, but it would have been money thrown away on unlimited. So for me the 2GB plan is perfect. If I happen to go over it an extra gig is even cheaper than the first 2 were ($10 vs $12.50). But so far Have not even come close to going over it. And I really don't watch how I use 3G--if there is no wifi I use it, no worries.
As more people like me quit this club those using a boatload of data each month are going to be harder and harder for AT&T to justify. And by boatload I don't mean 2GB-5Gb per month. I mean 8-25GB per month (yes, I have seen people use 25GB!).
But kudos to those who persevered. Sometimes I miss the old club!
Michael