Re: What shows are broadcast in 5.1 digital surround?
My receiver has this scrolling display that indicates a new audio signal format coming in. When detecting Dolby 5.1, it will scroll "Dolby Digital 3/2.1" from right to left.

CBS does a six channel stereo effect when outputting shows not originally in true 5.1. The local and national newscasts, some (not all) commercials, etc.
Pretty much all prime-time shows are in 5.1, with results different with each show's individual mix.
For example, CSI: has a great mix of the title song, but the majority of the show is front-heavy except for scenes in the morgue which have nice reverb of people's voices.
LOST has very low surround activity, which is a shame because of how atmospheric the show's environment is.
Eleventh Hour had fantastic surround activity during a recent episode opening with a big rain storm. Very enveloping.
My personal preference is to more 'aggressive' surround mixes, so occasionally I turn the rears up more than usual if I don't hear anything when watching something with the default settings.