I originally had our team append the URL with ?source=website...
Christine, there's a cool trick in this area that (I think) almost nobody knows about.
If you want to transfer one data point from the URL to a lead field, like lead source in your case, and you don't know the possible data values (or don't want to manage them), add that data point as the s -- just the letter "s" -- query parameter. (Like how you were trying to use the source param.)
http://landing.example.com?param1=whatever&s=linkedin
On the page, fire a simple Munchkin event. In the url include the name of the lead field you want to update to the value of s. Here, Munchkin is signaling that you're setting the lead field utm_source to the current value of s ("linkedin").
Munchkin.munchkinFunction('visitWebPage', { url: '/dataValueTransfer/utm_source' });
Your Smart List watches for any visit to /dataValueTransfer/...
... and your Flow sets data values accordingly:
The advantage of this quick-and-dirty method should be easy to see: the value you're putting on the lead is available as a special trigger token {{trigger.Search Query}}! (The s query param is the old-school way that search engines would tell you the search terms the user entered, back when they didn't care if you knew.) Since you have the token, you don't need to know the possible values, so it's a lot like a form post with a single field. It could contain any value at all (s=blee, s=blah, s=somethinganoutsideagencydidnttellyouaboutbutthatsokay) and that value will get popped into the corresponding value on the lead.
Anyway, food for someone's thought, I hope... not a fit for more complex situations but I thought I'd share it!
Note: You can actually adapt this same technique for multiple values per page view, though in uplevel browsers only. Since that excludes IE 8-9 I won't include the method here to make sure everything is compatible.
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