BizTalk Server 2006 Beta was just released a few days ago.
Click here to learn about the improvements and new features in BizTalk 2006. At the bottom of the page, there is a link that will bring you to the page where you can sign up to get a copy of the Beta1 product.
Specifically in BAM area, the new features incldue support for messaging tracking, a public managent web service, portal and alerting etc. There're some improvements in the infrastruture as well. One of them is that you can add new activity items to an existing activity w/o the need to first undeploy everything.
Note that you can deploy BAM tracking infrastruture to Yukon SQL database in Beta1, but not to Yukon Olap analysis database yet. The support will be added in Beta2.