Please note I have WP_DEBUG set to true.
When you click the "New Layout" button on the "Appearance->Theme Options" page without typing the name of a new layout, you get an undefined index notice:
Notice: Undefined index: active_layout in /option-tree/includes/ot-functions-admin.php
Not a major problem because it works in a normal (non developer) setup, but is worth fixing for future :)
This notice then causes a Warning: Warning: Cannot modify header information
Not sure if this is where I'm supposed to let you know about bug fixes, but hey ho :) Awesome plugin anyway, keep up the good work!!