Simon Roth, developer of space colony sim Maia sent a tweet out recently showing some sales data, Linux is doing reasonably well.
Here's what he said:
So far this year 4.9% percent of people buying @maia have been Linux users, OSX coming in at 4.4%. Biggest regions are USA (32%), UK (14%) and Germany (11%).
When I asked for more information, he said this is the reverse of the last quarter, when Mac was higher than Linux. Good to see Linux pull ahead slightly there, although it's worth nothing the actual amount of copies sold likely isn't too high, he said last quarter it was only about 700 units.
Even so, Mac and Linux together making up nearly 10% of their overall sales is certainly nothing to sneeze at, especially if you're not making a huge amount of sales, to me that says they're quite important.