We use it for payments on our website, and it allows quite a bit more functionality... for example the IPN receiver is still used, but it's really just a for notices about future events. The event (payment) happening NOW is done in realtime via a token that's passed back.
You can do a lot of other useful things directly from the XF admin control panel (no need to log into PayPal's site)...
- Manage recurring subscriptions (we can make an API call to find out if the user has/has not canceled their subscription... and we can edit/cancel if we wanted).
- Allows you to process refunds (both full and partial).
- PayPal transaction searching
- Pre-authorizations (authorize an amount for capture in the future).
The API itself is SUPER easy to use and integrate (see first link in this post).
It could allow advanced things even that end-users could use (for example cancelation of a recurring subscription without needing them to log into PayPal and find their subscription transaction). It could also be used for less vague subscription expiration emails (since we can find out if the user has or has not actually canceled their subscription).
It also allows for better management in the admin control panel directly without needing to flip back and forth between there and PayPal's website.