I take care of two Rottweilers during the week for extra cash. One of them had bad, bad genetic defects in both her hind legs causing her knees to pop out of the sockets. Long story short, the owners couldn't put her down, so they had her legs fixed. Now, they both need a baby sitter. The male (and not the broken one) is 110lbs. The female with the bad legs is close to 90. When those dogs go at it, I almost don't want to be in the way. The big one glanced my leg at full sprint and just about sent me head over heels. Big problem with Rots, or at least these ones is that they're so territorial. Any other dog, person, etc... walking down the street sets them off in to full bark mode. The drool is pretty damn bad, but they are still fun to play with.
If anyone is thinking about getting a Newfoundland, I can put you in touch with a guy that comes into the Starbucks I work at, because he runs, or helps run an organization in Northern California dealing with the breed.