Just wanted to let everyone know that Donne's sermons (based on the Potter and Simpson edition) are now available online -- with some nifty bells and whistles -- at {http://lib.byu.edu/donne/}. And should you ever lose track of the URL, we have linked it on the Donne Society's "Related Sites" page (itself linked at the top of the page you're reading).
What a great resource. However, it seems that the text lacks the marginal notes that are present in the Potter & Simpson edition. Am I missing an online feature that shows them, perhaps as metatext?
No, you're right that the sermons online lack the marginal notes, textual notes, etc. It's still a great resource, but as with all online resources, use with care.