Adam, we have been using iframes to display our Marketo forms, but recently needed to embed one on an external page. I followed the instructions on the
Put a Marketo Form on a Non-Marketo Page help article, but the resulting formatting was horrid including no red asterisks after the labels indicating required fields. Also, the help article indicates that you need to use an iframe for progressive profiling and pre-fill.
So I found this article, inspected your example landing page (thanks for leaving it up there!) and discovered a few style sections that you had included that were not shown in the help article as well as a couple of scripts defining the profiling. After adding the missing code, the format was perfect, and the profiling and pre-fill worked as well!
Unfortunately the form's hidden fields that would populate with cookie values when the form is in Marketo are not being populated when using the embedded form :0( We have the javascript on the page that allows the cookie value to be read, but we need to use a token in the "value=" portion below - does anyone know what that token should be?
<li class='mktField' style="display: none;"><label>utm_medium:</label><span class='mktInput'><input class='mktFormHidden' name="utm_medium" id="utm_medium" type='hidden' value="none" /><span class='mktFormMsg'></span></span></li>