Andy Schatz's Pocketwatch Games trumpeted the news on Twitter, saying total sales are around the 520,000 mark, and only include about half of the total HIB 11 sales - at the time of writing the bundle's sold 270,000 odd. Monaco is a "Beat the Average" purchase in HIB 11, meaning it's a bonus for those who spend more than the average spent on the bundle.
Monaco hit and ran onto Xbox 360, PC, Mac, and Linux last year, but eight months ago the sales news wasn't as encouraging. Back then, Schatz noted he was disappointed with the game's Xbox Live sales, conceding the parts played by an underwhelming demo along with the delay that prevented a simultaneous release alongside PC.
That said, there should be plenty more Monaco sales to hit over the next fortnight, with Humble Indie Bundle 11 not set to conclude until March 3.