For users that are diving into customizing their installation and using the PayPal addon, here is a utility function that will allow you to determine if a registered user is pending (i.e. they have not yet paid). This can be useful for content display that you may intend for any registered user regardless of payment status, or some other use.
I use this function on the rocketgeek.com site to display information on which posts are free and which a only for paid premium users. This information displays if the user is not logged in OR if they registered and are logged in but did not yet complete payment.