as far as I can see, it seems to work.
When press the Express Checkout, it goes to Paypal, gets the User Information and goes back to pp_confirm. Finish shopping, it goes to the success page.
Now I only need to update the User database table. where do I put that? At the "pp_checkout_success". Just with Dataassist ON PAGE LOAD? Or do I have to check again if the payment is right?