When I had a computer I had heard that heavy internet users would be throttled to help with traffic. With my cell phone when I had exceeded downloading over 1Gb, my service would be throttled. At first I couldn't figure out why (I thought that Cricket was having a problem), later I learned from technical about Cricket's throttling policy (to this day the store dummies staff still don't know what throttling is).
This story has a happy ending for me. Cricket amended their policy letting me download without throttling (for more money). I reasoned what happened with me is happening to others so I put up this guide.
Eventually there may be no more throttling as there's Verizon FIOS and its equivalent coming out plus 4G LTE for phones coming out as well. So if the service is slow, you can check with your ISP.