Hemisphere Games analyzes the sales numbers for their Linux port of Osmos and ask themselves, 'Is it worth porting games to Linux?' The short, simple answer is 'yes.' Breakdown and details in the post."
A few other interesting details: the port took them about two man-months of work, the day they released for Linux was their single best sales day ever, and they got a surprising amount of interest from Russia and Eastern Europe. Their data only reflects sales through their website, and they make the point that "the lack of a strong Linux portal makes it a much less 'competitive' OS for commercial development." Hopefully someday the rumored Steam Linux client will help to solve that.