Not much, but at least a couple of basic shaders to get started with can also be found between my open sorce engines files:
the .vsh files contain the vertex shaders and the .fsh files the fragment shaders, but I guess thats selfexplaining...
On current mobile hardware, you should do as much as possible within the vertex shader and the trick for great looking and fast games is to write many very specialized shaders doing always just exactly what is needed to make something look the way it is meant to.
At least thats my experience with my iPhone 3GS, which features the same gpu as the iPhone 4 but has less pixels to do deliver data for. This is most probably already much better with tegra 2 and even better with apples A5 chip, but for now, this means that you should not try to port shaders for desktop gpus to mobile phones and expect a great performance :P
This also means that fullscreen effects, especially on devices with a high resolution display tend to be slow.
Hope this also helps a bit :).