[Brian]

OmniFocus' attachment support is basically what Cocoa's Rich Text support gives us; you're going to see similar (and similarly finicky) behavior from TextEdit since they share the same underlying code. If you see differences between OmniFocus and TextEdit, that's a different matter.

If you add a couple of file attachments to a TextEdit document, then add some text, you'll see that you're able to multiply-select files and/or text and then drag it over to OmniFocus' note field. You can do this in the other direction, as well. Both apps are putting the file attachments on the clipboard.

If you drag that same selection from TextEdit and drop it on the Finder, you'll get a clipping that contains the text, but not the files. It appears that the Finder discards file attachments when it finds rich text data on the clipboard.

I'm not sure if the attach-one-file thing is another case where there's an external limitation or not; looks like this is the first request we've gotten for the ability to multiple-select there. I'll file a new feature request. Thanks!