Adelphia does not cap users on the amount of data you download, however immense routing issues are present in OH/VA/MD/PA and other locations which won't seem to get fixed. One of the biggest problems lies within' the 68.168.17.109 & 68.168.17.110 routers, pushing latency numbers up to 200+ before even hitting the backbones.
I suggest you read
http://www.dslreports.com/forum/adelphia on current Adelphia issues and switch ASAP if possible - Did you know they're bankrupt?