I once worked at a bank where someone got in trouble for checking her e-mail from work. It was a consultant I was working with, and she was checking her legitimate work e-mail through a web interface, but it was still a violation of IT policy to check outside e-mail. She was even checking her mail over SSL, but the IT department noticed her behavior by analyzing traffic patterns, not by actually seeing the contents of any of the traffic she was sending out.
That's just what I thought of when I saw meebo repeater today (via Venture Chronicles). I imagine that sooner or later someone is going to get fired for using this. If there's one thing that I know about big corporate IT departments, it's that they hate to be fucked with.