After I signed up through the link in the OP, this is the message I got:
Congratulations! You’ve signed up, so now you can start earning 5% cash back on your holiday shopping after making your first purchase with PayPal.
Look for the PayPal button on your favourite websites and start shopping.
Then I got an email:
THANKS FOR SIGNING UP
Now that you’ve signed up, all you need to do is make
one purchase with PayPal and you’ll start to
GET 5% CASH BACK*
on every purchase you make after that, until
December 10, 2012.