In the past I've worked with CRMs (perhaps some higher ed folks remember Hobsons Connect?) that included a Source field for Constituents. If someone first came into our database by filling out a webform that would automatically populate on their record, and if I uploaded a list of prospects that would be a required field. As far as I can tell, RE does not offer any native way to track this other than the Added By field, or a custom field. It is hard to look at RE and answer questions about where our Constituens are coming from. Blackbaud talks about mapping donor journeys, but for many of my Constituents it would be hard to identify where their journey started.
I'm curious if this comes up for anyone else. Do you have ways of identifying where you are getting your new prospects and donors? If a bunch of people sign up for your email list at an event, do you have a way of saving that data to their records? Do you try to understand the journey's of individual donors? How do you use RE or other tools to answer these questions?