I was wondering this too. I've chased leads on several ways to download an inventory as a starting point for the new City set I added here (http://rebrickable.com/design_set?s=60152-1) and nothing seemed particularly straightforward. The inventory on Brickset was claimed to have been downloaded from Lego and corrected, but I couldn't figure out how to import from there to here, and I was also uncertain about how to get the details directly from Lego, or even from Bricklink. I had thought that puzzling through it myself would help me know how to do it in the future, so I kept investigating whenever I had the time. My next step was going to be to see if I could figure out a way to translate between the Brickset CSV and the Rebrickable CSV... but now I see this:
...which seems to imply that you high-level studs might have access to an easier way, and that this thread really is a place to ask for help with getting a preliminary inventory into the set listing. I am happy to wait patiently and to help check it over when it's here, but I'd also love to know if the steps you take to get the inventory from Lego are things we really could do ourselves, and what I might've missed when I was looking for it. All I saw was a page where I could click 299 times to get the pieces into a purchase order, but that really didn't seem like the best way! If there is a way for us to do it, could the steps be added to the FAQ? Or if there is too much risk of us messing it up while trying and cleanup of the mess too cumbersome, could that info be explained in the FAQ?
Thanks again to everyone who is working on making this awesome site even more completely awesome!