I would find it useful to select a plain text, rtf or formatted note and “Open With” DEVONthink Take Note. Why? Because Take Note can float above all app windows and spaces and act as a very useful scratch pad – so it would be great when my ongoing note-taking is interrupted to return that note to the Take Note interface and take up where I left off.
(While I’m at it – it’s now 2014 and so it is time to get rid of the horrible Take Note HUD interface with the Smoke theme 
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I’ve requested in the past that I would like the ability for Take Note to reopen with the last note to use as a scratchpad similar to what you suggest. However, if you are in DEVONthink and want to ‘Open with DEVONthink Take Note’, you can somewhat accomplish that now. Type the hotkey to open Take Note, and drag the text file that you want to use into the note field of the HUD. The text of the document will appear in the note field. The downside is that, once saved, a new note is created instead of having the changes applied to the original note. Which could be a plus if you want to maintain revisions.
I have also requested, many times now, to dump the HUD interface. Please!!!
Yes, it’s that downside of duplicating notes that makes the workaround less helpful. Another workaround is use nvALT (or any NV clone) and index the notes – but without a haxie the nvALT panel doesn’t float on top.