SharePoint Lists vs External Data Sources (BCS/External Lists)
1. BCS Limitations
http://chakkaradeep.com/index.php/bcs-limitations/
2. Using SharePoint workflows with Business Connectivity Services (BCS)
http://blogs.msdn.com/b/bcs/archive/2010/01/20/using-sharepoint-workflows-with-business-connectivity-services-bcs.aspx
Using SharePoint workflows with Business Connectivity Services (BCS) – Sandboxed Workflow Actions
http://blogs.msdn.com/b/bcs/archive/2010/01/29/using-sharepoint-workflows-with-business-connectivity-services-bcs-sandboxed-workflow-actions.aspx
Using SharePoint workflows with BCS – Full Trust Workflow Activities
http://blogs.msdn.com/b/bcs/archive/2010/03/02/using-sharepoint-workflows-with-bcs-full-trust-workflow-activities.aspx
3. http://blogs.msdn.com/b/chaks/archive/2011/05/02/concept-leverage-sharepoint-workflows-with-external-lists-part-1.aspx
Differences between native and external lists
http://office.microsoft.com/en-us/sharepoint-help/differences-between-native-and-external-lists-HA102771000.aspx
SharePoint Lists vs. External Databases
http://msdn.microsoft.com/en-us/library/ff798319.aspx
Notes:
1. How to: Use Business Connectivity Services with SharePoint Workflows
http://msdn.microsoft.com/en-us/library/office/ff394479(v=office.14).aspx
