The general rule I've always heard is that it needs to make 3x the production budget in its worldwide gross to break even theatrically, in order to account for marketing costs. Which means if it gets past $270mil it will be in good shape, since most movies barely make a profit 'til they hit home video markets these days anyway. It could get there since there are a few international markets it still hasn't opened in, including Japan, which is generally pretty big on Spidey, and its far from done domestically, too.