I have tried many systems to export my comcast address book to the Ipad without success. The sync worked for my files but not the contacts. I used carbonites "sync and save" and also tried manually joining the 2 devices. I am one frustrated old lady.
Follow this guide to export your contacts from Comcast in the vCard format (VCF): http://www.watchingthenet.com/export-address-book-contacts-from-comcast-webmail.html
Then, email the vCard file to yourself. Open that email on your iPad and download the attachment. Now you will have your Comcast contacts on your iPad.