I've done some searching for this on your site and found a few posts from two years ago asking about PayPal Payments Pro (Direct Payments) for Marketpress and Appointments + but now that I've installed them I don't see any support for this.
You've got Paypal Express Checkout which is required when using Paypal Payments Pro but no PayPal Payments Pro plugin?
It is a great payment solution, low cost, especially for low volume stores and easy to setup, and the best feature is the checkout stays on the site.
Can we have it? Or has someone else built it as a separate plugin? I bought the complete annual WPMU subscription but this is a showstopper.