After a drop shadow is initially created, is there any 'added' performance hit compared to a PNG image drop shadow? In other words, are drop shadows 'baked' after layout and creation?

We don't bake anything by default in Noesis (by design, to get good performance without spikes). But we have plans to implement something like BitmapCache in the future.

OK, if they are not baked this means that images with built-in drop shadows perform faster than a Noesis drop shadow, right?

Yeah, I would say so. If the content is static and you don't need it to be resolution independent, baking the shadow is going to give better performance.