I am in the same boat with Matthew Miller. Here are a few things I found on the GUID he refers to:
- This seems to have a lot: REST API - create contact and link Eloqua GUID
- How to repost an externally hosted form to Eloqua (Part of Step 2. Also check the comments)
- Getting the GUID on external pages and other hidden options.
- Eloqua API How To: Submit A Form
- How Does Form Integration Work?
I know that's several things, but thought it might help. This is a HUGE part of the benefit of Eloqua. By linking up the cookie GUID with a form submission you are able to take a LOT of anonymous data and tie it to the contact (whether they are new or existing).