Since Windows Phone 7.8 was released today for some devices, the folks at XDA-Developers have already capture the URLs for the CAB files that are downloaded via Zune. That means anybody can download them manually, and then use the "Cab Sender" utility to install them to any Windows Phone 7 device in the same way that your Zune desktop software would. Be sure to read the instructions in the first post of the thread to learn how to install the update correctly. You must send the proper CAB files to your phone in the proper order and it is very important that you include the correct language CABs that are associated with the languages already pre-installed on your phone (when a particular build update includes updated languages that is). Those are a couple of mistakes that people often make.
DISCLAIMER: Using this method will likely void your warranty and can potentially brick your phone, so proceed at your own risk. If you want to stay on the safe side, just wait until the update comes to your phone through the normal Zune interface.
While reports are showing that the update is being pushed to a wide variety of first and second generation Windows Phones, are you patient enough to wait or brave enough to try the manual updating method above? We're hearing that the cab sender method is successfully working on plenty of devices like the Samsung Focus, Dell Venue Pro, Sprint HTC Arrive, HTC Mazaa, etc.