As per all the rest -- I am happy with two-channel dvd. BUT, I use full-range bi-amped speakers (get stereo sub) AND speaker positioning has to take into account the screen, as there's no centre speaker (positioning isn't much of a hassle if there's enough room anyway).
Furthermore, for the outlay of 5-6channel HT, one can afford better two-channel equip.
So, until 5+ channels become mandatory, by law or otherwise, we're OK with two...:)