Here's why AJAX suxx:

TCP for JavaScript instead

Hard to believe after all the humbug enhancements that have been done on top of HTTP somebody finally comes up with the utmost brilliant idea of simply letting applications do TCP.

This is neat, since PsycZilla would then be able to become a normal webchat rather than an application, and still use full-fledged native PSYC.

The apparent security nightmare is non-existant: Java applets and recently even Flash movies already do native TCP. All you need is a security mechanism like crossdomain.xml. So why keep JavaScript from doing this, too?

WHATWG server-sent DOM events

New stuff of this kind. The spec says:

This interface does not allow for raw access to the underlying network. For example, this interface could not be used to implement an IRC client without proxying messages through a custom server.

Well, then why are you doing it? Who needs yet another AJAX?

See also

HTTP, server push, Comet and the POST superhighway.