Re: In my experience ...
"... allowing ordinary users to interface with test systems in the comfort of their own desks is asking for trouble."
I disagree. For one - getting users to help you is tricky , so getting them to relocate makes it harder.
2) it makes a more realistic simulation , as seen in this case
I think in an ideal world the users wouldnt even know they were testing - you'd just ask them at them of the day " any issues today?"