ZuneScene is guilty for setting Zune's Wifi (almost) free:

1. Rename the extension of any file to .jpg
2. Drag and drop the file into "received pictures" using Windows file explorer.
3. Send the file Zune to Zune as if it were a photo. In this case we had to send an entire folder. We sent 4 good photos and one .pdf file with a .jpg extension. If the single (fake) photo is sent alone an error is detected. 
4. The receiving Zune should sync with the Zune software. The file can then be opened in it's containing folder and renamed to the original extension.

I believe Zune must be checking the first 3-4 photo's headers if they are valid. A program that adds jpeg headers to other files types and then removes it could be a very good idea to bypass Zune's Wifi restrictions once and for all!

EDIT: this can be used to of course to bypass the 3 days 3 plays restriction on Zune. People still call this "Wifi DRM". I remind you that Zune just marks the tracks sent wirelessly for 3d3p it DOESN'T encrypt them with DRM (if they are DMR-free of course).