It would be infinitely helpful to be able to mark a contact as being me. This would allow applications who want my information (word processers, Devkit, any app that autofills your info) to automatically use it without prompting me.
In addition, If Dexter is going to sync with Facebook and other sites, it seems that there should be a "Unified Me" contact. That is, a contact of the user they he/she edits, and the information in that contact is then pushed out to all of the services with which that person has Dexter sync. This, to my knowledge, is not done by anyone else at present. This saves us the trouble of going to each social service/address book service/place where we have a personal profile and manually updating say a phone number. All we would need to do is go into the "Unified Me" and edit something, and those changes are then sent out to everywhere.
Evolution currently grabs information from the "about me" information GNOME grabs during install. Integrating in a similar way would be worth looking into.