When I submit a comment or vote on a comment, then want to immediately comment or vote again, I get a(n annoying) message that I have to wait 5 or 30 seconds. Couldn't you just set a timer on the server that wakes up in 5, 10, or 15 seconds and completes the request I just sent instead of making me resubmit the request after waiting. You'd may (or may not) need to use the AsyncController to do this. Couple this with a modal dialog on the client that dismisses when my request has been completed and you've accomplished the same purpose without me having to submit things twice. I think it would be a much better user experience.
Update: To prevent gaming the system, you'd want to keep track of pending requests and flush any new requests of the same type while a request is currently pending. A user simply using the system, i.e., waiting on the modal dialog to dismiss, won't notice this behavior, but a user who submits, then refreshes to gain the ability to submit again more quickly would be blocked.