The US Patent & Trade office, on 2/14/2006 granted a patent for AJAX to a small firm out of CA.
The abstract of the patent says the following:
A host computer, containing processes for creating rich-media applications, is accessed from a remote user computer system via an Internet connection. User account information and rich-media component specifications are uploaded over the Internet for a specific user account. Rich-media applications are created, deleted, or modified in a user account, with rich-media components added to, modified in, or deleted from the rich-media application based on information contained in a user request. After creation, the rich-media application is viewed or saved on the host computer system, or downloaded to the user computer system over the Internet.
This is rather vague, as patent applications can often be and still be approved. To date, there are no known lawsuits that may have been filed for patent violations. Here is a link direct to the patent filing for AJAX. This could have implications for Adobe's Flex technologies as AJAX is used for sending content to clients (as with many of the latest crop of rich multimedia environments that are emerging in the marketplace).