So AtomPub is a reasonable way to publish things, etc. Would be nice to push an AtomPub endpoint to a service as a callback for events. An awfully large number of things can accept HTTP now, and there is a reasonable basic-operation system available, so why not take advantage for callback APIs? Instead of polling a site for updates, post a subscription with an AtomPub endpoint as the entry and let the service push to you. AtomSub :-)
writebacks...
DOS
So what about denial of service attacks? Subscribe someone to a few million blogs and it could start to cause some problems for their endpoint. PubSub.com was doing something like this, but with Jabber endpoints. There's also the Feedmesh project, which nothing public ever came of, but I'm under the impression there were a few fairly large private meshes happening for a while (not sure if they are still active, though)
Yeah, I prototyped something like this a couple of months ago using Abdera. I used APP to create the subscriptions using atom entries containing some XML describing the subscription (url, timeout). It was remarkably simple to do the simple things, and was pretty easy to extend to most of the WS-Notification scenarios.
This guy seems to be working on a very similar idea. He calls it web hooks and doesn't limit it to APP. http://blogrium.com/?p=70
comment...