I really liked my last pair of 811's because of the very breathable mesh uppers. I can't comment much on the tread, but it didn't strike me as especially good or bad. They seemed slightly less durable than some other shoes I've backpacked in, but considering how comfortable and breathable they were, I guess it's a bit of a tradeoff.
I'm using a pair of 812's now ( http://www.nbwebexpress.com/newbalanceMT812AT.htm ) which I haven't tested much so far, but my initial impression is that they're less breathable but they seem more durable. Still very comfortable, though. If you plan on using 811's, you might want to buy them soon because I believe they are being phased out in favor of the newer 812s.