After updating to ICS I had the same comcast email failure. Turns out, that in the email settings, SSL is on by default. Change that to "none" in both, incoming and outgoing. Comcast does not use SSL. Incoming is Port 110. Outgoing is Port 587. Then launch the email app and see what it does. Should sync and work. If not, then there is some other issue or setting that is preventing it from working.
if you can't change ssl & ports, remove then re-create the account.