Hey there Jamie. We've had pretty good luck with the bit of scripting that I inserted. It was kind of a rush job, so it's definitely not module-worthy, but it fits our needs pretty well. I wrote my own control panel for ZC because we do a lot of custom reporting. The custom db table records the order number and the tracking code, so I just added a join in my SQL queries to compile things like order total, items, and tracking codes.

We do a lot of search engine advertising on google, yahoo and msn as well as some banners and affiliates, so it's imperative that we can trace orders back to the advertising. This concept was pretty simple to implement and so far it hasn't caused any problems other than adding a step to the ZC update process.

Here's the over simplified logic:
1. attach a tracking code to the url (domain.com/index.php?tracking=code)
2. in index.php, sessionize $_GET['tracking']
3. in checkout_success, grab the order insert id and insert the tracking code into a custom db table

I think the concept is module worthy. I haven't written any modules yet, but it can't be that tough, right? This feature is definitely worthwhile. If anyone wants to start a 3rd party module project, I would be more than happy to help out!

Kevin