After spending several hours working on a PDF form, I saved it using skim, expecting it to save the form fields that I'd filled in. I've now lost all of that data. I'm now aware that I should have "saved as copy" (And of course, I should have tested the save feature before relying on it).
In order to avoid such a situation for other users, I suggest that when users try to save a document with filled in embedded text fields, that skim warns the user that embedded text will not be saved!!
Thanks --- I've been very happy with Skim up to this point!