Well, I'll definitely preorder it from Amazon. Seeing as how this doesn't come out until nearly three weeks after the movie, I'll be cancelling it if I don't like the movie, though.
I'll give it a rental but am waiting for the huge mega set that I'm sure we'll get once the movie itself comes out on Blu-ray/DVD.
IIRC - this was content that was originally suppose to be part of Watchmen but was cut out due to length so there is also some speculation that this might show up in a Director's Cut of the film.