You might have logged back in before PayPal sent the payment notification. The perk has definitely been applied to your account. This is not an experience that I want anyone that donates to have, so I'll be making some changes today to streamline this process a bit.
The first of those changes is that the confirmation page will now automatically apply the perks without having to log out and back in again. Please re-visit the confirmation page if you still don't have the "No Ads"-perk:
I've now added a loading indicator to the confirmation page as well. Note that this will only work if you just donated, if your donation was more than a few hours ago it will keep showing the loading indicator.