Guido convinced me that having StopAsyncIteration inherit from Exception was the right approach, as it means errors are more likely to be of the "we caught it when we shouldn't have" variety, rather than the harder to debug "an exception escaped when it shouldn't have" variety. This isn't like SystemExit, KeyboardInterrupt or GeneratorExit where they're specifically designed to reliably terminate a thread of execution.

That means I can offer an unreserved +1 on the current patch (#6) for beta 1 :)