I think it should against the LAW to say "unlimited" and then place a limit on it. It's bait & switch, pure and simple. I think they should have to pay a fine, reimburse the customer somehow and then give them the unlimited they signed up for.
I think the average person has no idea what 5GB is so perhaps it would be an interesting commercial to show the layman how much internet is involved in a 5GB limit. "5GB -- that's a 1,000 songs or 10,000 web pages or 15 full length hollywood movies" -- something tangible so that people who don't know will understand that it's a lot of data. At least that way, the carrier isn't just lying to the country when they say Unlimited and then impose a cap on it.