That means LittleBigPlanet is probably the biggest PS3 game, taking up 40 GB, to date then...
http://dlb-network.com/2008/09/littlebigplanet-takes-a-lot-of-big-space-40gb-on-blu-ray/
I think Heavy Rain might be the first game to actually fill the blu-ray to the brink with original content (no padding, no videos, just the actual game), since there is a ridiculous amount of assets going into that game.