The August SharePoint SDK is now available and has some good stuff for interop. In particular, the refreshed SDK includes the new Business Data Catalog (BDC) Definition Editor, aka the BDC tool.
The BDC is the set of metadata that describes the various LOB systems that can be accessed from Sharepoint apps. One challenge with the BDC is that the tooling support for it was not good - it was difficult to add or edit systems into the BDC. It was MANUAL xml hacking, yeck.
This tool addresses that problem, which should make lots of Sharepoint devs very happy.
Check out Brian Coyne's blog post for more info on the BDC tool.
In the near future you'll see the Sharepoint team deliver more prescriptive guidance around connecting SharePoint to LOB systems. We started with SAP but will be expanding to Oracle (Siebel, PeopleSoft) and others. Check the Sharepoint Interoperability site for details.