It's clear that speculation is still the driving force behind the exchange rate fluctuation, with over 130k BTC changing hands today on Mt. Gox (only ~10k BTC mined per day). So assuming all of the BTC mined on any given day are thrown into the market, they were traded 13 times each!
This is some heavy heavy speculation... but we know not all the BTC mined are traded right away. As a first estimate, I'm going to say 50-75% of BTC mined per day are either hoarded or used in some way on the web.
Let me know what you think ... and share the info!
Used on the web, basically means sold on MTgox, any retailer is just trading them in for currencies they can pay bills with.