Does anyone know where I could find information regarding the nubmer of seats for each of the FEA packages?
e.g. 10,000 seats ansys, 7,000 abaqus, 9,000 Femap, etc.
Worldwide? You may find some figures knocking around on the web, but I wouldn't expect a massive degree of accuracy on this - regardless of the source. I could be wrong, but you'll probably find figures posted on the big boys' websites stating "more than ##### clients" etc., but I guess it would be very difficult to actually obtain a true figure for the number of seats from ANSYS/ABAQUS/NASTRAN/etc.
but I'm not sure how much I would trust the numbers. The other question is should you break Nastran down into NE, NX, and MSC (among other ones like AlgNastran, AINastran, etc.)
And then there's the additional confusion of academic seats (or for that matter pirated ones). And then there's organisations that have license servers and worldwide operations, so they can easily have 3 users per license.