An interesting implementation of this might be with GET variables in the URL, like the way Google Analytics handles campaign, keyword and medium sources. This would require crafting separate URLs for twitter, Facebook, and anything else you would want to track.

Here’s an update on this thread… Trying to import IDs into a list. I have a CSV with nationbuilder_ids and state_file_ids of people who are already in my database – I’m just trying to import them to a list based on search criteria I queried offline. However, when I’m trying to map the fields on the import, state_file_id is not one of the fields available in the drop down, and when I try mapping only nation_builder_ids, it says that that is not sufficient to make a match. So, 2 issues to report:
1) state_file_id is not a field option
2) unique matching should only require a nationbuilder_id