As a follow-up to this question, I think having user-settable dates for newsletter delivery would be a nice feature. Seeing as the newsletter already automatically cycles through days for delivery, letting users choose their own dates would be quite useful, in my opinion at least.
One use for this could be to sort newsletters by topic. At the moment, my Stack Overflow newsletter is being delivered on Thursdays, and my Programmers newsletter on Tuesdays. I would prefer if I could set both to be delivered on Monday (Programming Mondays, if you may). Also, I'm sure at least some people would find it useful to get all their newsletters sent on one day instead of spread out throughout the week (the way that the newsletters originally functioned).
Just my 2¢ worth.