I guess it depends on the specific architecture, if you use something like Mongrel2 messaging is used for everything, even for routing HTTP requests and respons

I guess it depends on the specific architecture, if you use something like Mongrel2 messaging is used for everything, even for routing HTTP requests and responses to the processes/servers that handle it. Also, hasn't it always been the case that a lot of web applications communicate with the database directly to fetch information? What's so "web 2.0" about that? The major thing that changed with AJAX/Comet and Websockets and such is that the javascript running on the end user's browser can now be regarded as an endpoint for message-passing. This increases the amount of messaging, doesn't it? In so far that relying on just polling a database is no longer good practice in our "realtime notificiation" world...