There's a fascinating interview here (1 hour long) with the people who did the visual effects on the film.
http://io9.gizmodo.com/this-one-hour-conversation-about-the-vfx-in-star-wars-1753538070
I went with my two sons to the iMax in Waterloo to see it today and so glad we waited until we could get good seats at that cinema. The 3D effects worked well and we felt fully immersed in the film - well worth the hassle of catching a 7.30 train to 3 Bridges, bus to E Grinstead and then train...