Looks like a pretty cool product, especially for those who want to add on small real-time features to their application but don't want to have to deal with evented servers/browser support/etc. I started looking into doing something very similar about a year ago based on having those exact needs actually (the project was eventually scrapped).

- The cost is listed as per million messages - what happens if I deliver 900,000 messages, what am I charged (if anything)?

- Care to share any details about your infrastructure?

- Have you thought about writing (and open-sourcing) a simple demo app, such as a chat room, to give people an idea of how everything works together?