My point is, you totally should. I am friendly with my coworkers too, if I want to have a non "work-friendly" talk with them, we talk in the kitchen or at the pub. It baffles me that people would use a work provided form of communication and _not_ assume it's auditable in some way.

edit: should clarify that my work is probably more calm than most and would probably not GAF about it regardless.. but it's just good opsec. Never write something down you wouldn't be comfortable having read out to you if it can be traced back to you.