Almost anything; they won’t GPL their driver like they ought to, because they made unwise decisions surrounding the use of material covered by software patents and non-Free licenses, and thus are unable to do so.
Aren't they re-architecting & creating a new, free software driver that's only responsible for memory management & conveying requests from the user through to to the _real_ computer running on the GPU?
Don't clutter up this thread with actual facts and information.