As computer generated effects become cheaper and more realistic (and easier to reproduce), they invevitably become more commonplace. Exactly how commonplace may suprise you though. Take these two SFX showreels for John Adams and Boardwalk Empire, both recent HBO dramas. Their use of multi-layered CGI and green screen techniques is impressive.

It's not just period dramas that get this level of CG attention though, just have a look at this showreel from Stargate Studios, responsible for effects sequences in many big TV titles.