First, there's a lot of aggregated data available online. Second, I think the traffic stats for chromeOS are so small right now that it probably wouldn't make it out of the 'other' bucket on most sites that don't specifically target the OS as an audience.

Who is the ChromeOS audience anyway? My perseption is that it's pretty general: Students, 2nd computers, postmen, etc. A lot of tech-savy people seem to buy them as an extra machine or just for fun.