If you registered a ps3 early access code you can only log in from ps3. If you registered a pc early access code you can only log in on pc. I know because I had two early access keys and I used one on pc and one on ps3. You will see permanent service option called "Preorder Ps3" or something similar to that if you use ps3 early access code and "Preorder PC" if you used the pc early access code. If you are legacy and preorder ps3 then you should be fine.... Or if you have two preorders code you will be fine...
EDIT
Ok I am at my post limit. So I'll just edit this post. Here is how it will work:
Use your early access code for the platform you want to play on!
The ONLY exception is if you are a legacy player (not a non-legacy 1.0 player). In which case you will automatically get PC early access and thus don't need to worry about not wanting to play on ps3. OR if you have 2 early access codes.
EDIT2
OK NOW ALL 1.0 PLAYERS THAT APPLY ANY EARLY ACCESS CODE TO THEIR ACCOUNT WILL BE ABLE TO PLAY ON ANY CONSOLE. IF YOU ARE NOT 1.0 THEN YOU ARE STUCK WITH THE CONSOLE YOU REGISTER. THANK YOU BAYOHNE!!!!!
FINALLY IF YOU DON'T HAVE PS3 CLIENT I WOULD GET THE PS3 CODE OR YOU WON'T GET CLIENT (for 1.0 players only!!!)