It's a separate product from MobileMe, yes you will be charged. I would assume that by the time it goes gold, it will have considerably more features than it does now making it worth whatever they charge for it (which I assume will be less than MobileMe).
They better do something good with the beta if they want to start charging people, cause I don't see anyone who'd be willing to pay for some annotation stuff, when they can get much more full-featured stuff from Google and the like.