Thanks Elliott. Yes, I can see the possible duplicates smart list and unfortunately we do have duplicates. This was primarily due to some issues with Salesforce for Outlook (which has since been fixed) creating duplicates in SFDC that then synced over to Marketo.
I understand what you are suggesting with creating a new smart list but it really does not solve my issue as I am talking about 8000+ leads that need to be on my list and it is not easy to figure out which ones have duplicates.
Let me ask this, if I import a list of email addresses for which there may be duplicates, will all of the leads with that email address show up on my list or just one?