I didn't see anywhere specific to add a suggestion or "realy like to have" posting for FileMaker, so here goes:
I would LOVE the ability to alter the tab alignment for tab controls. For example: to have the tabs align like a notebook on either side of the element, or heck even beneath the element.
A cool extension of this would be the ability to have say, a group of tabs for each tab. Each tab along the top of the element could have its own set of tabs aligned along the vertical edge(s) o the tab control element. This could add a TON of usable space to a layout by taking more advantage of the z-axis (stacked layouts).