Collect aggregate stats of total hidden service usage vs total exit usage in Tor network

I'd like to know what fraction of total Tor usage is hidden service usage, so we have a sense of whether hidden services matter now, and so we can track trends into the future.

For example, it would have been nice in August 2013 to have some metric of hidden service fraction that told us the spike in load and users had to do with hidden services.

Such statistics would also be useful to counter (or who knows, confirm) the analysts who say statements like "97% of Tor use is silk road".