I don't think Greenlight is intended to be anything approaching a democratic or automated filtration system. It strikes me as pretty much a transition from all submissions going straight to Valve - through the mountainous pile of which they must then wade in order to find 'Steam-quality' games - to them first being posted on Greenlight for some community feedback. Valve will retain final say and need not pay any more attention to popularity of any one given submission than they deem is appropriate on a case-by-case. Essentially, it would seem to me, they've simply added a layer to try to help them deal with the deluge.
It's not dissimilar, in fact, from the way Arcen operates with adding new features to their games. Personally, I think Greenlight - done properly - can only be a good thing.
Yea, I think it would be good for us, though our existing relationship may bypass the need, we'll see.
In general I think greenlight is just their way of "sorting" submissions for their consideration. Basically when they have time to evaluate more submissions, they'll start at the top of the pile and work their way down. Not quite that simplistic, of course, but I imagine that would be very helpful to them.
But I imagine the actual evaluation would be much the same as it has been, just with "better" (for some definition) prioritization.