I was hoping to use the SFDC Lead field 'Created By' for those leads that are created by specific Sales Reps, and then add them to a specific Smart Campaign in Marketo.
Unfortunately, I found out from Marketo Support that this isn't possible, but this is what they suggest:
The Salesforce "Created By" field is not part of the Marketo integration. If you want to see that information from within Marketo you'll need to create a custom field and have a process in Salesforce write the actual User's Name into the field. You don't want to user a lookup/rollup for the custom field as this will result in the User's SFDC ID being recorded in the field and synced to Marketo rather than the User's Name.
Thanks Sam, exactly my question. It's unfortunate that this is the best solution available right now.
As this field never change, you can just use a formula (text) field in SFDC with the following formula on leads and contacts:
CreatedBy.LastName &", "&CreatedBy.FirstName
The hard point is to have the filed value to flow to Marketo just after creating the field, since it will not be pushed to Marketo until all leads and contact are updated.
In order to do this, use the technique describes in the comments of this post : How does Marketo see and pull data from Salesforce Formula Fields?