Oh they are and they'd keep the gravy train going, but it appears like a lot of people are stepping off it at least here in the US.
One sign of that was the opening weekend for Pirates 4. 3D ticket sales here in the US were down to 47% of the take. Kung Fu Panda 2 was 45% of the take. Both movies were expected to draw 60% of their ticket sales from 3D.
A complicating factor, of course, is that 3D apparently remains wildly popular overseas. Whether or not that's enough to sustain it, who knows, but I suspect the trend will be for only the big tentpole movies to bother with the 3D process like what we're seeing with IMAX.