I live in London, and our broadband has no caps or limits. No idea what it costs though since it's included in my rent. Speedtest results:
My folks, however, live in rural Australia. Landline broadband is not an option so they're limited to mobile access using a USB modem.
Coverage is patchy to say the least. They can pick up one provider only in the living room (but nowhere else in the house) and another provider only in the bedrooms. So they are signed up to both ISPs and have a USB modem for each one, switching depending on the part of the house they're in.
I've also seen them run the modem out the window on a long cable and stick it on a chair in the backyard to get better reception... and put it in a little plastic lunchbag if it starts to rain.
Don't know what the speeds are like, but my little bro plays online games over that connection so I guess it can't be too bad.
When the family lived in town, they used a broadband plan where you were "shaped" if you exceeded the download limit - the ISP just limited your download speed until the month rolled over. Downloads during off-peak periods (some time in the late evening til 6am) weren't counted towards the quota. If a contract must involve a cap, I think this is my preferred option. It seems less painful than being cut off entirely, or charged an additional fee.