I'd suggest that if someone loves this concept -- a meta-service that works between service and client might be very useful. Similar to FeedBurner. Users would

I'd suggest that if someone loves this concept -- a meta-service that works between service and client might be very useful. Similar to FeedBurner. Users would have a central location they could add their hook urls to. (Drop-down: service/method to hook/account credentials.) They could establish preferred formats, like XML or JSON and this service could translate from the primary service. Services could talk to the meta-service via a queueing system, so scaling would be simple. The meta-service could go free and make money by offering to do SMS messaging or email messaging for clients with a subscription.