I just read that the 508/608 have HDMI passthrough so audio signals can be played through the TV speakers if I don't want to turn the receiver on. This is a huge plus for me since I have little kids - although I always want to run things with the full audio, if they are sleeping or we are just watching a kids show, I don't have to have the receiver on.
So far, I am leaning toward the 508. Only thing it doesn't have is analog upconversion but my only analog signal is the Wii, which to me, isn't really worth upconverting (I do use Netflix streaming but use my HTPC with HDMI out). Powerwise, I think it should sufficient for my needs.