I have been in a similar situation to many, using wifi at home and only using about 100-250mb of internet usage a month. I don't see how I could go near the 500mb if I wasn't doing it deliberately. Since I heard about this situation though I've used about 300 in the past 2days.
I think, why should the people who use the data responsibly get punished by having to fork out if they ever go over the 500mb. Also, on a personal note I am still quite near the beginning of a 2year contract (what's that all about anyway, TWO f-ing years tied to the same contact just to get the device you want). Cutting the contract short will allow me to save a lot of money, plus allow me to upgrade when I want, not when they tell me.
So-sending a message to the corporate big boys AND saving myself cash- what's not to like about getting out of your contract early?