This is how you make a services app: Besides the obvious TV guide listings, Comcast's mobile app gives you integrated access to your Comcast email, voicemail and missed calls and lets you sync iPhone's address book.
You can forward calls from your Comcast number to your iPhone, and it pulls voicemails from your Comcast home phone and Comcast email into a single inbox. (Though why you'd use the email inside of Comcast's app over the iPhone's actual email app is beyond me.) It'll also sync your iPhone's address book to a universal Comcast address book. The program guide is nice enough, with bookmarks and reminders, even if it's not the flashiest TV listings setup we've seen.
I got the occasional error message that the app ran out of memory, and it'd be nice to be able to do some account management, like order On Demand movies for later from my phone, program my Comcast DVR box, or pay the bill.
Overall, it's a surprisingly nice little app, provided you actually use your Comcast email address and have their Digital Voice service as your home phone.