Nintendo video does not do anything with trailers... trailers are still seperate downloads.
Nintendo video automatically downloads new videos, which you can play inside of nintendo video.
I currently have 2 3D cartoons, and 1 magic show. Total runtime is ~15 minutes. (One of the cartoons is 8 minutes long... well, 7m52s) Download is pretty quick, quality of the cartoons is excellent - some graininess in the magic card tricks.
It says on each video that it is only available until 20/07, probably the date on which new videos arrive to replace the current available ones.
All in all: well worth the money (0 bucks). It's pretty nice for a free service (even though, as far as free services on consoles are concerned: Vidzone is still my favorite) --- Do you believe in the Soul Cake Duck? Einstein: My wife doesn't understand me.