There are plenty of reasonable concerns over this merger, but I really don't think the badge--although it has gotten LOTS of focus here--is one of them.
I came across this on the net several weeks ago and can't find the site, but there is apparently an old legal doctrine--I believe it's actually common law but it goes WAY back--that the writer of this other post said might apply in badgeware cases. I can't remember the exact Latin phrase, but the essential meat of it was "One cannot prohibit what he has elsewhere required." It's one of those provisions that, like the Magna Carta itself, force even rulers to be under the law.
In our case, this means that since we are bound by a legal contract (the Zimbra and now Yahoo public licenses) to display the Zimbra logo, Microsoft or Zimbra or Yahoo themselves cannot suddenly say "Oops, now you are no longer allowed to use our logo" and thereby prohibit us from fulfilling a contract into which we entered legally and in good faith.
Microsoft (or Yahoo!, for that matter) could stop development of the Zimbra product. They could refuse to release those parts of the software that they own, that are not under any public license. They could fire the whole Zimbra team lock, stock, and barrel. But what they can NEVER do is simply yank the rug from under the whole shootin' match by putting the clamps on their logo.
As I said at the beginning, there are plenty of REASONABLE causes for concern in all this, and I'm no happier than some of the rest of you that there has been so little information from those that know. Unfortunately, when lawyers and non-disclosure agreements and corporate confidentiality and bureaucracy get in the way, the flow of information to us, the masses, tends to suffer. C'est la vie.
Now time for the requisite disclaimer:
But I still think you all should lighten up on the badgeware issue--there are potential problems, but this ain't it!
I am neither a Zimbra/Yahoo/Microsoft employee nor an attorney. I am speaking entirely on my own behalf and at no one's prompting. I am doing my best to relate a legal statement I read somewhere, as a layman who could have it all wrong.