It would be a very, very hard thing to measure - and do you equate a desktop clock utility with a full-blown 3D animation application, for example? It turns into apples and oranges.
I think there's quite a lot of closed source apps that run on Linux - many of them are specialized things that work with apache servers in mind, also scientific and technical things like liquid flow analysis. Stuff many of us would never have heard of, much less know what to do with.

I'm not as ballsy as TM and won't provide a specific percentile range

, but my gut sez that I'll bet it's probably the inverse of Windows.
DT