Update: Lollipop is now available OTA on Nexus 7!
Why? Why not? This will remove any custom boot loader and wipe the tablet. I did this from Windows 7 – in Linux its pretty much the same but doesn’t require the Google USB driver and you can obviously extract the image using tar from the command line.
Download the Android SDK, run the Android SDK Manager and install Google USB Driver (from Extras) and Android SDK Platform-tools (from Tools). The former are installed to AppData\Local\Android\android-sdk\extras\google\usb_driver by default. If you’re unfamiliar with USB drivers Google have a guide.
Your device’s boot loader needs to be unlocked then boot in to the boot loader (hold down power and volume down button when turning on).
Add the location of the Android SDK platform tools to your path will speed up the command line part. Open a command prompt and go to the folder you extracted the image to.
Check that the device is recognised by typing fastboot devices – if there is an output then all is well. Now run flash-all.bat – this takes a while (159.617 seconds on my Samsung RV511), when it is complete it will reboot the tablet. Rebooting took around five minutes on the first boot.