When the Humble Indie Bundles are on sale (where consumers can pay what they want), the stats showed the average Linux user paid more than Mac or Windows users.
I don't think that necessarily carries over. For the most part, all the Linux users I know contribute more simply because they want to encourage other developers to create games for Linux. It's a point of price, they can point at, and say "Hey, Linux users spent more then Windows or Mac users."
