The examples for sending from django, python, rails, etc are really neat! I wouldn't have thought of directly sending querysets, but the simple example made it seem obvious.
I hope you find the right paying niche for it. I personally wouldn't pay $20/month for it unless I had an active startup project. For me, a couple dollars a month maybe since my use would be pretty limited and occasional.
See also http://mondash.org/, which is much simpler, but similar in some aspects.
Consider my comment invalid from now.
Generally everything is possible, since we are now learning how the users would like to use the service. But the SaaS model is easier to manage, and there are successful monitoring services that use this model (www.stathat.com).