Anybody? This question comes up in the discussion history with no answer.
Adobe Digital Editions does not have an option for exporting these items.
However, it does write these out to plain XML files that you can find on your computer. The location of these files should be something like C:\Users\bhaugen\Documents\My Digital Editions\Annotations\.external except replace my username (bhaugen) with yours. There should be a file for each book and the file extension should be .annot but they are really just XML files. I am not sure if you can copy these back into Adobe Digital Editions somehow but you would at least have the content that you created.