I often use the transparent forms in web sidebars (e.g. Wordpress widget area). The form is contained in an iFrame and space has to be provided below the form to allow it to expand to add validation messages (and prevent the submit button from disappearing).
I would love to see a styled version of the validation messages so that validation messages just pop-up and hover over the relevant field.
Here's an example (just click in a couple of fields and hit the submit button): http://tinyurl.com/dxnz4s7