Investigate why it looks like there at most 500 bridges
Mike asked why it looks like there can be at most 500 (or 512) bridges in the Tor network:
https://metrics.torproject.org/networksize.png?start=2010-08-01&end=2010-10-12
I think this is coincidence. I'm attaching a graph that doesn't have daily averages, but has a data point every 30 minutes. There doesn't seem to be an upper bound to the number of running bridges.
Mike, does that answer your question? If not, can you ask someone with access to BridgeDB to investigate further?