I'm beginning work on an effort to integrate BizTalk with Dynamics AX 2009 via the BizTalk AIF (Application Integration Framework) Adapter that comes with AX 2009. I don't have a lot to post just yet as we're just getting started, but I'm looking forward to learning more, as there's not a whole lot out there yet about the AIF adapter. AX is also capable of communicating via messages through the AIF to MSMQ queues and the file system, but its cool to see such great support for BizTalk - the adapter install is included on the CD with the product, and includes hooks into the "Add Adapter Metadata" wizard in Visual Studio so you can connect to an AX instance to generate schemas and port types automatically. The adapter and the wizard are very tailored - really all you need are login credentials and the name and port number of an AX instance, and you're off and running.
From what I've done so far (the walkthrough in the newly-updated white paper), from a BizTalk perspective it's pretty simple to get set up and running, and the fact that AX uses fairly simple XML is a big plus. The white paper walkthrough has you creating orchestrations for the purposes of synchronous communication (optional, as async is available as well and probably preferable for most everything) as well as correlation for an asynchronous exchange, but its easy to see how you could do it all without orchestrations for simple one-way messaging.
The white paper is here. If you are at all interested in getting BizTalk and AX 2009 to work together, this should aboslutely be your very first stop. This white paper isn't like most others - it's an instructional walkthrough that covers every step, from AX configuration to building the BizTalk solutions from scratch. Unfortunately, the prerequisites/setup are awful. At the minimum, if you have a valid login at PartnerSource, you'll be downloading many gigabytes worth of Virtual PC images (2 of them), and you'll need decent hardware to run them both at once (I wouldn't touch it with a 10 foot pole if you don't have at least 4 GB RAM, or separate systems you can use to run each image). If you don't have PartnerSource access, you'll need to set up Dynamics yourself, or obtain an already-set-up image from another source. I highly recommend getting the images from PartnerSource if possible - setting up Dynamics is a major activity, requiring a domain and lots of other server resources.
More posts regarding BizTalk and AX are forthcoming.