@Joe yes, there are really 2 ways to come at this challenge of tracking lead sources and I recommend pursuing both in parallel because they yield different insights:
cookie-ing and storing the UTM params with the contact record so you can analyze where the leads you have came from (what the plugin I shared above does for you)
using a tool like Google Analytics (or preferably something like Mixpanel or KissMetrics) to log events for site visitors and be able to run aggregate analysis on how people are moving through your funnel
The first answers the question “how did this guy/gal originate?” at the level of the individual contact.
The second lets you slice & dice data in aggregate on visitors regardless of if they signed up or not. It lets you ask questions of the data and find answers as well as conduct “fishing expeditions” where you’re just noticing aberrations and patterns that you hadn’t set out to find.
Mixpanel is REALLY powerful in this regard. You can log any kind of custom property you want for the user (basically think “anything that’s a tag in AC should be a Mixpanel property as well”). MP tracks all their history before you even have their contact info and then marries it up after the fact so you can see all the history prior to having the lead. It lets you run cohort and funnel analysis and they have a whole section called People where you can test theories after the fact (you’re basically logging every event and unlike how GA forces you to define the funnel ahead of time, you can test a theory you didn’t have initially - the data is all there).
Anyways, I recommend running this plugin in conjunction with Mixpanel. Create a free Segment.com account and a free Mixpanel account. Install the Analytics WP plugin, wire it up to your Segment acct, add Mixpanel project as integration in Segment then start to tinker in Mixpanel reports. Even if you don’t perform any analysis today, start tracking stuff now so you’ll have the event logging for later. You will be glad you did. good luck