Pocketwatch Games tweeted that sales of Monaco: What's Yours is Mine has surpassed half a million to date. This includes roughly half the Humble Bundle sales as Monaco is only given to those paying above the average price for the bundle.
"Sales update: We're well over half a million units of Monaco sold! (~520K), only includes about half the HIB sales since we are BTA"
The tweet was posted 8 hours ago, and Humble Indie Bundle #11 is currently very quickly closing in on the 300,000 mark so surely Monaco is racing onwards towards even greater milestones.