Blu ray may allow for 7 channels... but very few titles have it. That isn't to say 7 speakers in a good sized room wouldn't benifit from the two extra speakers, but don't add those channels with the expectations of hearing a lot of discrete sound coming from them... yet \:\)

This site is pretty great for statistics:

http://www.blu-raystats.com/Stats/TechStats.php

It shows of the 1935 blu ray titles with a known audio type, 135 of them have 7.1 audio. I've gone through that list and there are countless titles in that list I've never heard of.