This mod will allow you to send any type of file (EVEN MUSIC!) using Zune-to-Zune WiFi, Bypassing the 3-play / 3-day restriction.
Estimated Mod Time: 1 minute to transfer to your Zune
Mod Difficulty: Easy
Information & Setup
This modification requires that the initial sender of the files had completed the zune as a portable harddrive mod.
http://www.zunemods.net/Zune_Portable_HDD_Mod-va6.html This mod involves nothing more than renaming files, and the standard Zune-to-Zune transfer method.
Step 1 
Rename any files you wish to transfer, to "filename.jpg", where filename represents the original, or desired filename.
Step 2
Drag all of your .jpg files into the "\Storage\Received Pictures\" in your Zune device. If that folder does not exist, create it.
Step 3
Send your files through the Zune-to-Zune image transfer.
NOTE: You must send at least 1 real picture (sometimes more real pictures are required. It all depends on the amount and size of the fake image files being sent).
Step 4: Transfer Recipient
All the recipient must do is connect their Zune to their computer, and find the files (under the images section) and rename the files back to their proper extension. Example: if the file was originally an .mp3, change the filename back to "filename.mp3".
Conclusion
Now, this may seem like a lot of work just to transfer files to your buddys, and it is. But for the time being this is the best way to transfer files of any kind wireless Zune-to-Zune. Hopefully in the future when the Zune Firmware gets a makeover by Microsoft, or modded by users it will simplify the process to send files via WiFi.