Todd Baginski has a great series of how-to posts that demonstrate multiple capabilities of Business Connectivity Services. These are the posts on Todd’s blog so far:
This blog post discusses various business situations where you may need to create a SharePoint 2010 external content type programmatically, and describes how to do it.
This blog post describes how to create a SharePoint 2010 BCS .NET Assembly Connector to read data from a flat file and register it as an external content type in SharePoint.
This blog post describes how to register an external content type associated with a .NET Assembly Connector with the SharePoint search service to index and search the data coming from the external content type.
– Lionel Robinson, Program Manager