There is a chance the OTA will fail, as this have happened to some users already:
You might be able to recover if you have USB Debugging turned on PRIOR to performing the OTA update. (Will need to flash factory image).
The problem is the factory image will require you to unlock the bootloader to flash it. To unlock the bootloader, you need to enable USB Debugging. BUT if the OTA fails, you can't boot into the OS to enable USB Debugging. You will end up with a brick.
Here's my experience:
I enrolled my Nexus 9 in the Android N Beta Preview program, and a minute later I got a notification that I have a system update. I went through with the update like any other update. I got to the part where you see an Android laying on it's back and it says "updating system" (or something to that effect) and it has a progress bar. After a few minutes, I see the same Android on it's back, but with an exclamation mark and the words "ERROR!". It would then reboot itself after a few minutes later, but get stuck at the Google logo.
If you leave everything stock, unrooted, and bootloader locked (like a good user), don't try to get the preview via OTA without enabling USB Debugging first! This way, you can at least be able to flash the factory image if the OTA takes a dive.
Since I bought the tablet on Amazon, Google is washing their hands from tech support. Instead, they gave me HTC's support line (which is currently closed). I don't know what I will have to face tomorrow morning when I call.
UPDATE: Google posted signed OTA zips that can be used to recover from this situation. You can now use adb sideload to side load the full OS in OTA form. Go to https://developer.android.com/preview/download-ota.html to download.