I think instead of being able to advertise "up to" speeds, ISPs should have to advertise the overall average speed you can use in a month taking into account usage caps.
150GB/month works out to .47MBit/sec sustained throughput. If AT&T had to advertise that rate instead of 6Mbit for DSL lines, they'd think twice about caps.
UVerse is even worse--~1Mbit/sec instead of 24.