Sorry, I guess I should try and contribute a little more than a smartass comment.
Oh, that's a point
Being in the UK, any physical incentives seem to go against donating since they would consume some of the donation to post. So for example the DVD option in Aaron's one seemed interesting, and I donated enough for it, but didn't actually go for that reward option.
So any downloadable incentives like the actual plays, sneak previews, art or assocated fiction are always a cooler option to me. Not sure what my tipping point would be for donating a little more just to include fiction though. The benefit of the actual plays is that I tend to listen to them at work, out and about, and on journies, so they get repeated listenings. Any other goodies are less likely for me to increase a donation to acquire.