Salesforce Customer Portal is the Force.com ISV’s natural choice for providing support to users of their applications. However, requiring customers to log in to a Customer Portal using a Salesforce username and password which is separate from their own Salesforce login can be cumbersome. It doesn’t have to be that way.
Learn how FinancialForce.com achieved Single sign-on to our customer community from within our apps. My walk through was recently posted on the DeveloperForce Wiki: Salesforce as an Identity Provider for Customer Portal.
Please give me a shout if you have any questions!