Where I work we have a number of pre-defined email lists, all of which are prefixed by a departmental prefix: XYZ-Finance (~10 people), XYZ-Travel (similar) etc. and XYX-All (~2k). I've lost count of the number of times some-one has Auto-completed to XYX-All instead of XYZ-SmallGroup. I would sneer, but I'm afraid I've done it too. I'm pleased to say that on receiving one of these I've never replied to all to warn the perp of their misdeed though, another all too common occurrence.