With Virgin Media, it is "Limitless", but if you download anything big during peak hours, they put you on the "slow-internet", for 3 hours. So the best thing to do with them is to play games and the like during stream hours and save the downloads for off-peak.

Even then, I am apparently on 100mb/s and I only seem to get speeds of 400kb/s on most downloads such as Steam. (when I downloaded Team Fortress 2 last night)