>Is any buffering in place? Is it possible, for example, that a user might be double-clicking on a link rather than single-clicking, thereby sending two requests in quick succession? Just SWAGs...

Well, if that would be the case, I wouldn't have that much duplicates. I have a lot and this is continuing day after day.

>Off-topic: the other day I participated in the survey for screen resolution. The pop-up browser window went away, as expected. Later, while in UT I used Crtl-N to open a new browser window, and I got another survey window ! Does this mean I could have voted again, or do you enforce "one user, one vote"?

We enforce the rule.