Flex Data Services for AJAX
I this link on Ben Forta's blog about a new project called Ajax Data Services on Adobe Labs.
This Library lets you embed an invisible SWF file in your web page, and then use Flex Data Services to push data to your HTML content. It is extremely difficult to push to AJAX clients without a technology like this for developers.

Hans, are you aware of the free, limited-production version of Flex Data Services Express 2? It would probably suit the needs of most. The couple of limitations are listed here:
http://www.adobe.com/products/flex/productinfo/faq...
Adobe lists the following prices for FDS;
FREE/Express (commercial-use product limited to 1 CPU implementations with no clustering)
US$6,000/CPU for Department Edition (100 concurrent users)
The enterprise version is the most expensive version. The way most companies do business, this cost is passed off to the customer.
US$20,000/CPU for Enterprise Edition