It's quite clear to see that on the right, my oily lids have consumed all the eye shadow, causing it to crease and even completely disappear in patches. It's worth mentioning that this is the bit of creasing left over from the very end of the day, as I did attempt to re-blend the creased shadow back into place a couple of times today (which clearly didn't work). On the left, however, the primer has held the shadow in place perfectly. These photos were taken after about 12 hours of wear.
So, if anyone ever asks me if Urban Decay Primer Potion really does work, I will continue to wax lyrical about its virtues, and now I have the photos to prove it.