By "definition" the first Beta may well be the last one, but by experience, it would probably take one or two more betas before the final release.

More importantly, however, and this is why I am touting this "first beta" thing so much, is that there will be an upgrade script from 7.0 to 7.1beta1, and if there're more betas - the will be interim upgrade packs. So, one can potentially start using 7.1 from the first beta, in case they agree to put up with frequent updates and see more potential beta-stage issues.