From ZuneRama forum : 

As part of Windows Updates on my laptop today, I installed an optional update called "Driver Update for Zune USB."  It actually installed a pre-release version of the Zune 2.0 software with a version number of 2.1.0522.00.  Has anyone else gotten this update?  I have it running now, and so far, all it does is list music in my library.  When I connect my Zune, the software sees its name and knows it's connected but will not sync.  Just curious if this is Microsoft pushing out a beta, or some kind of accident.

[...]

It looks like most of the features aren't working, I can browse music in my personal library, but I can't access anything on the marketplace, the categories are there but everything else is blank.  I'm going to leave it open for a while and see if it starts downloading marketplace info.  I'm wondering if I somehow got the update by accident and it actually isn't ready to use yet.

[...]

I didn't get hold of the software illegally, I think it was accidentally released to me through Windows Update, though I don't know why no one else has seen it yet.  I'll probably uninstall it and go back to Zune 1.3 if the marketplace doesn't come up in a day or two.  Anyway, I guess it gives us an idea of what we'll be looking at.

And the photos: 

 

Here is an official photo of the Zune Software v2.1, released by Microsoft, to compare it against the above: 

I triple-checked my Windows Update, but there is no present there for me

Links:
The photos in full detail

[via CruchGear ]