It all depends on the cost of the plan. Right now I'm paying $45/mo for Qwest (now CenturyLink) DSL, which apparently has a 250 GB cap. My other option would be Comcast, which would be $60/mo (no cable TV service) and carries the same 250 GB cap, albeit with faster speeds than DSL.
If the 50 GB package is significantly cheaper, then fine. Give people who don't use as much the option of paying less. If not, fuck that, quit trying to sell me less service for more money. I'd be really pissed if CenturyLink all of a sudden decided that my $45/mo was only good for a 50 GB cap at some point in the future.