This would lead to Anthropomorphism, which is a bad idea. Besides, that would crap creep many users out.

Users want computers to do as they ask, not to socialize with in an attempt to convince them to do as they want. When you address someone in a first name basis, you are communicating on a personal level, something which users don't expect computers to do. Imagine if you used your face to log in and your computer commented

This would lead to Anthropomorphism, which is a bad idea (*). Besides, that would creep many users out (**).

Users want computers to do as they ask, not to socialize with in an attempt to convince them to do as they want. When you address someone in a first name basis, you are communicating on a personal level, something which users don't expect computers to do.

(*) If your computer refers to you on a first name basis, wouldn't you feel that you have to reply in the same manner in return.

(**) Imagine if you used your face to log in and your computer commented the your hair looks good today.