Sorry, but I don't believe a single word of it. A mild depression (dysthymia) is known to result in increased perceptive accuracy for your reputation, abilities and the like, and therefore might indeed improve written communications, as a consequence of the "depressive realism" hypothesis. However, there are also indications of an opposing effect taking place --the increased rational self-control typical of dysthymia only works satisfactorily for trivial, mostly in-lab situations. You cannot rationally control every aspect of any real life situation, and therefore any complex enough communication will be equally botched (or brilliant), grumpiness or no grumpiness. Here's an abstract for you: http://bit.ly/1rnXn9
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And have a nice & shiny day!