I just got my Nexus 7 today, and I am trying to root it using adb. It always shows my nexus as offline. I have tried updating my adb (It is version 1.0.31) I do have usb debugging enabled, I have tried reconnecting it to different usb ports. It has not ever shown the prompt for the rsa fingerprint, which I believe is the problem. Any help would be greatly appreciated!
I finally fixed it by deleting the adbkey and adbkey.pub files in my .android folder, killing the adb server, unplugging my nexus, revoking USB debugging permissions, plugging my device back in, and starting the server. A prompt asking me to confirm the computer's rsa key came up, I accepted, and now it works!