I've done this with my sister from different rooms in the house... It was quite common to get an IM from her in the bedroom that says "bring me a soda" since my CPU was closer to the kitchen than hers!
I've also done similar things while tagging MM with anghara13 and she was merely a simple five feet away! open_the_blinds and I do so randomly, but usually just sharing links or exchanging graphics while she's here. Broadband is a good thing to have with graphics.