I don't want to sound like a PubNub shill, but I was able to integrate PubNub's publish and subscribe system into an App Engine app in about an hour.
They've got a free development tier, and offer a free production tier if you're willing to incorporate PubNub branding in your app. http://www.pubnub.com -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to google-appengine@googlegroups.com. To unsubscribe from this group, send email to google-appengine+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.