Comcast's email system is fully functional and working, I get my mail every day, all day.
When you say you tried accessing comcast.net from your work PC, do you mean you went into your Xfinity Connect mailbox? Where there any messages there? Where you able to access the Inbox?
In Mac Mail do you have any filters setup to move or delete incoming messages? Have you checked your other folders? Do you have the option set in the account definition to leave a copy of the messages on the server?
Have you tried sending yourself a message? Does it ever show up?
Have you activated email forwarding? Even if you haven't, I would suggest checking that setting at:
https://customer.comcast.com/Secure/Users.aspx
