Oh, I touchtype, or close enough anyway. Typing capitals has little or no cost. But to capitalise on IM, and to use fullstops, now seems overly formal to me, inappropriate in casual conversation with friends.

It's quite fascinating, really, how these things develop. For example:

  friend: seen reddit today?
  me: no # <-- devoid of further meaning, a neutral tone
  me: No. # <-- overbearing and formal, almost a put-down:
        "No, of course not. Stop wasting my time."

Language, and its contextual use, evolves rapidly and I would now argue that capitalisation and full stops in IM have taken on a different meaning than when used in regular prose.