I just had a similar chat with RCN before finding this thread. Here is a snippet from the log with more detailed information as well as a recommendation to use a VPN client:

17:25Jackie S.: We are aware of the problem customers have been experiencing. Our engineers have investigate the problem and found the issue is between ORMUCO-WebHost) and ONAM.
17:26Jackie S.: Since this is not an RCN related issue, we do not have an estimate of when you can expect a resolution. I apologize for the inconvenience.
17:27Jackie S.: We were receiving lots of comments about it so we made sure to look into it.
17:28Jackie S.: If you connect through a VPN, you may be able to get through. Unfortunately RCN can not provide techinical support for a non-RCN issue.

I live in Chicago and my local friends playing with RCN service are also experiencing the issue. Good to hear it's at least been acknowledged by my ISP and they've located where the trouble is emanating from.