I have not yet replaced all my 1.4 machines with 2.0, but at the moment I am behind a 2.0 production machine and have had no show-stopper problems at all since deployment, some weeks back. This machine does the basic infrastructure and network stuff, site-to-site VPN, and some simple file sharing. Everything has worked pretty much as advertised, right out of the box. I am a no-tweaks type of user, so there has been no fiddling by hand involved.
So I personally have no experience yet that makes me think of 2.0 as a "production beta." On the contrary, so far I am appreciating the improvements over the 1.x line.
As for the bit about "quality assured" updates, I think that simply is an offer to minimize the risk of using an integrated solution. For example, back in version 1.0 or 1.2 (can't recall off hand), a standard DansGuardian update through the Ubuntu repositories broke eBox Internet connectivity (if I recall correctly). The eBox/Zentyal developers worked it out pretty quickly, but anybody who rolled out the change to a production machine in the usual way was in a little trouble. We had some lengthy discussions about how to deal with the problem, including some sort of automated ability to roll back changes (again, if I recall correctly).
I understand Zentyal to be offering an alternative to the stock internal process of rolling out changes to test machines before going live, or to some sophisticated roll back process. They appear to be offering to take the testing step for us, for a fee. I really think the weight of the risk is not so much on the Zentyal packages (though everybody makes mistakes) but more on the Ubuntu updates side of the equation, where a particular package update could unintentionally cause issues in an integrated system.