On most dedicated web based survey products (e.g. Zoomerang) there are facilities to create survey campaigns consisting of managed lists of potential responders. Invites are sent out, presumably with URL parameters that can identify them for tracking purposes.
I can see how some sort of solution could be found to overcome this, since all the internal functions to pass and process such scenarios is already in place. However it struck me that a better solution would be to have all the URL parameterization generated and managed by a campaign capability – as per my intro above.