A couple of charts from the stamps.com link.

Up to 8 ounces for the same $2.60 rate is nice, for a lot of transactions that will keep you from having to worry about the weight, but then that 9th ounce is 70 cents more... Buyers and you will want to avoid one chip too many to trigger that!

It's also nice that legal size and letter size flat rate priority will ship for the same price now. You can stuff a lot of stuff in the legal size envelope.