#1: ai is used in either Japanese or Chinese to describe 'Love'. In manga (or anime) it can be used to describe the genre, like in Gravitation, it would be called Shounen-ai or "boy-love" because it is about to gay boys.
#2: A.I. is the abbreviation of Artificial Intelligence...or androids (robots)
#1: Person A: "Hey! I just dropped by Borders and picked up a copy of Gravitation!"
Person B: "Cool...what's it about?"
Person A: "Well, first of all, it's a shounen-ai book. It's kinda like Japanese 'American Idol,... because the one boy..."
#2: The anime show Ghost In The Shell is about the future, where the difference between being a human or A.I. is almost indistinguishable.