Watched the French attract mode vid from one of the XBOX forums...once and once-only. Then deleted it so I wouldn't be tempted to watch it again...
(I couldn't resist and I figured it wouldn't contain any major spoilers as the Halo 1 attract vid really did not.)
I dunno about anything being considered even moderate spoilers in it (it was fast-cut), but it actually heightened my interest in the game even more. You do see some so-far unrelvealed 'stuff.' However, after watching it, I really am just going to avoid pretty much any new info on the game (unless it's an official video/news release).