To make your life easier when creating BDC application definitions you can use BDC Definition Editor that comes with SharePoint Server SDK. You have to install it separately after installing SDK. Installer is located in SDK installation directory. I had...
Recently I had to create Web Part connection between BDC based list and usual SharePoint list. BDC list was provider and usual SharePoint list was consumer. I was pretty surprised if found out that I was able to connect BDC based list only to other BDC...