Hey guys,
I just wanted to put some information together on how to recover your bricked Prime (if possible).

DISCLAIMER
I am in no way responsible for what you do with your Prime, even when you are following these (my) instructions.
There is always the risk of making it worse and this risk is completely down to you!!!

Currently we know 4 states of bricked Primes whereas 3 are more or less widespread.

• Brick 1a: You unlocked your Prime with ASUS’ tool, did some stuff to it (like flashing a custom ROM) and now it always boots into recovery instead of your ROM.
  You can’t select to boot to fastboot or anything else. No matter what you do it’s always the recovery. (happening to many users)
  -> Please go to Option 1a
• Brick 1b: You unlocked your Prime with ASUS’ tool, did some stuff to it (like flashing a custom ROM) and now once you want to boot your new ROM it shows you the bootanimation but suddenly tells you something about an “unsuccessful encryption” (it’s a real android screen, with a touch button etc.)
  Once you hit the “Reset” button it restarts but you can’t boot the ROM anymore, you are now caught in a CWM loop (much like Brick 1a)
  -> Please go to Option 1b
• Brick 2: When booting up your Prime hangs at the splashscreen (the screen with “EeePad” in the middle) and tells you something about an “unrecoverable bootloader error“ (happened so far to at least 4 users)
  -> Please go to Option 2
• Brick 3: (After messing around with your Prime in recovery it won’t boot any ROM anymore, you can however still access fastboot and the recovery)
  Update: This particular brick happens due to a bad kernel flash. If you are flashing kernels via the ASUS /staging method, make sure /staging is unmounted before flashing stuff to it, otherwise it WILL faill and brick.Update 2: It seems we can’t use the old fix for this brick anymore. Sometimes it does more bad than good. 
  ->Please go to Option 3

Option 1a  (This is the option outlined in my Video tutorial)

Don’t be afraid, your Prime should be recoverable. This is the good news. The bad news is, that you need quite some knowledge of ADB.

To recover your Prime (most likely) you need the following:

• A working ADB setup (please google that if you don’t have it, “tutorial setup adb” or something like that should do the trick)
• The USB-Cable to connect the Prime to your PC
• A few minutes time

Now do the following:

• Make sure your Prime is in Recovery mode (CWM)
• Open a cmd line on your pc
• Type: “adb shell“
• You should see a “#” now
• Once you have that “#”, please type: dd if=/dev/zero of=/dev/block/mmcblk0p4 bs=100 count=1and press [Enter]
• Now type: dd if=/dev/zero of=/dev/block/mmcblk0p3 bs=16 count=1 and press [Enter]
• Exit the shell and reboot your Prime via CWM
• It should not reboot to CWM automatically now. It either boots your ROM or is stuck at the splash screen. If it is stuck, boot to recovery and install any ROM you want. 

Option 1b

Good news, this brick should be no problem. 
Basically you need to first do Option 1a, but don’t reboot the Prime just yet.

• After executing the dd commands, you need to reboot your Prime to the bootloader menu andNOT the ROM itself.
• To do this you need to reboot your device while holding down the Volume_Down key.
• Once the white text in the top left corner appears release the buttons.
• Now don’t press anything until you can see a menu with 3 icons, an Android symbol, an USBsymbol and a Wipe Data symbol.
• Select the Wipe Data icon with pressing Volume_Down twice. Now press Volume_Up twice to reset the device to factory state.
• WARNING: OF COURSE THIS WILL DELETE ALL YOUR DATA!!!! EVEN THE INTERNAL MEMORY AKA SDCARD!!! CURRENTLY I DON’T KNOW ANY OTHER WAY TO RECOVER FROM THIS BRICK!!!
• After the wipe is done, you should be able to flash a new ROM or boot the existing ROM 

Option 2

Sorry, but your Prime is most likely hard bricked.
This can happen if you try to apply a stock blob file after you installed CWM. There is currently no way to recover from this. 

Option 3

If you are in this situation (Prime doesn’t boot but you can access both recovery and fastboot) please go to #asus-transformer on freenode and ask for help there. We currently don’t know if you can recover from this state.
Do not, I repeat, do not try to flash a stock ASUS ROM/blob file.
Doing this you will most likely hard brick your Prime.

We now found a way to un-brick this one too 
This one is a bit more risky, so make sure you follow all instructions with a bit of extra care.

Update: It seems the old method for this brick could make things even worse on some Primes.
On some primes this can be easily fixed, however putting this in a guide could do more harm than good.
So look at this thread to get help with this brick. 

Troubleshooting

• Problems getting ADB to work in recovery mode? Only seeing something like “Full Android on Emulator” in the device manager instead of your tablet?
  Well I have a posible fix for you: Got to this thread and download the drivers. Then override the drivers for the Emulator device manually with the new ones. ADB should work now 

— Read here how to prevent future bricks and other common problems —

Credits:
thx to kmdm for his solution on Brick 1a and Brick 3