Heh. Thanks! Rather than debug it I've spent the day porting the GUI to Daikon Forge. I can't say I'm regretting it. DF is infinitely more powerful than Unity's UI. I'm glad it forced me to make the switch.
DKForge is fine if you're targeting Windows/Mac, but if you're going to be targeting mobile I don't recommend DKForge at all. The performance was abysmal for me.
Having said that, they're working on DKForge v2 at the moment, which is being rewritten from scratch to be mobile friendly.
The unity 4.6 uGUI stuff was kinda promising. I did some tests earlier this week, and whilst it's buggy and some things just don't work properly at the moment, the ResolutionReference stuff worked great, and the performance was pretty great. I reckon in a couple of months when things have been sorted, uGUI will pretty good.