I agree with Mike. Virtually all (if not everything) of Tactical Theorems '10 applies to FM2011. I'd still consider it to be the best tactical resource for the game - and available for free.
Lee, just to clarify - that is not an FM-Britain guide. Yes, I am part of the production of it, but it's independent of my role at FM-Britain. It was written by Wonderkid, not anyone at FM-Britain. The other admins there have all looked to support/promote it though after reading it and seeing its value. That's why FM-Britain is. A review of it has been written by Gareth/Millie to go up on FM-Britain soon. (as it would be an obvious conflict of interest for me to review a book I took part in producing)