GPGPU. GPU performance is still increasing along Moore's Law, single-core performance has plateaued. The implication is that at some point, the differential will become so great that we'll be stupid to continue running anything other than simple housekeeping tasks on the CPU. There's a lot of capital investment that'd need to happen for that transition - we basically need to throw out much of what we've learned about algorithm design over the past 50 years and learn new parallel algorithms - but that's part of what makes it exciting.