I am incapable of not paying very close attention to someone who I am talking with. It's normally a nice thing but sometimes it can be a bit nerve-wrecking because it makes me extra sensitive and I may possibly read too much into their body language or the things they say. Luckily, I know this and therefore take correction well.
I do, however, daydream a lot. Mostly when I am in a relaxed state but never when I am talking with someone.