I've heard comments in the past (though mainly in the direction of Time Warner) that these types of limits could be used to push forth a internet providers own distribution service. They could conceivably place hard-caps on everything except for services they provide and attempt to lock you into their own services so you can avoid the crazy overage fees.
I'm not saying there is any real evidence for something like this to happen, just that the opportunity is there, and I wouldn't put it past a business to leverage a position like that.
In Australia, Telstra already does this. They run an On Demand Entertainment business (music, movies, games and sport) where the content is 'unmetered' (when downloaded it does not get attributed to your Usage Allowance). They also have exclusive rights to online AFL content (national league of Australian rules football), so you can't watch AFL matches, press conferences and various other things online unless you use Telstra as your internet provider.
FYI, you can see their exorbitantly priced plans here:
http://my.bigpond.com/internetplans/broadband/adsl/plansando...
Their overage charges are $1500 AUD per 10GB. Many A Current Afair story have been about some poor family slugged with a $10,000+ internet bill.
Since Usage Allowance's are so low in Australia, pretty much all ISP's provide unmetered value added benefits, like ftp mirrors and game servers. I had never realised that these kinds of thing were not net neutral. If these features were revoked, my internet bills would increase by 25%, which I obviously would not be too pleased about. Gah, now I am troubled; I'll be thinking about this all day.
EDIT: It appears these kinds of things are net neutral, because they don't restrict other people's packets.
There was a sentiment on the nnsquad [Network Neutrality Squad] mailing list that this could easily achieved using IP over ATM over optic fibre. You establish two ATM circuits: a public Internet connection that gets 1% of the bandwidth and a proprietary extranet that gets 99% of the bandwidth. Then, your ISP stalls and disregards network neutrality proposals. If you win equal access on the public bandwidth then it would only be a pyrrhic victory that obtains equal access to 1% of the avilable bandwidth. Meanwhile, your ISP could have a regional monopoly and have you beholden to any service which they choose to launch or not, at any price they choose, supporting any platform and DRM they choose.
I'm not saying there is any real evidence for something like this to happen, just that the opportunity is there, and I wouldn't put it past a business to leverage a position like that.