I'll start...
Likes:
Easy to use. Nicer Web Interface than last one. Decent size mailbox. Great Spam Filtering!!!! For an administrator of the domain, easy to setup and effortless to add people to the system.
Dislikes:
Wish the POP3 stuff responded to Client options - i.e. wish the messages would stay or be removed from the server based on the POP3 client's options that connect to it. All other email accounts I have work this way, but GMail is only configurable by the web interface and assumes you have only 1 POP3 client checking messages.