I wouldn't be so quick to say that RCN has no limits. Their disclaimers provide them the authority to throttle whatever they want whenever they want:
This is RCN's policy:
7.2. The Service provided is an ethernet-like IP service over a shared bandwidth connection, and users will contend for bandwidth. RCN will undertake reasonable efforts at network management, traffic analysis, operational procedures and user policies that ensure appropriate bandwidth at all times for as many customers as possible. HOWEVER, RCN EXPRESSLY DISCLAIMS ALL LIABILITY ARISING FROM OR RELATING TO ANY FAILURE TO PROVIDE ADEQUATE BANDWIDTH TO ITS CUSTOMERS. (the caps are in the original RCN document)
It's not clear whether RCN will throttle traffic for users who exceed certain limits. They've gotten into a little trouble in the past for doing that for users. I have no problem with ISPs doing a little traffic management, but the policies should be clear and upfront so that potential and current users can choose alternative ISPs as necessary.
Here's a link to a recent ARSTechnica article specifically about RCN:
»arstechnica.com/tech-policy/news ··· er-1.ars
I would hope that RCNman or another RCN rep can provide some transparency on current and anticipated future policies.