I always message people regardless of their status. If they're away, then they'll see it when they get back. If they're set to do not disturb, it won't pop up the window anyway, and they'll see it when they want to. If they're offline, they'll see it when they come online.
As for mine, my messengers are set to auto away after 5 min, so if I'm away from the computer for longer than a bathroom break, I'll be marked away, which is pretty accurate. People still message me, which I'm ok with, since I'm marked away they should know not to expect an instant response.
