One of the things we talked about a little yesterday, was mesh gradients. You can learn about them in all their glory by reading around page 253 in the PDF Spec, culminating with the grand king daddy of them all, the Tensor-Product Patch Mesh (page 276-ish). Once you can do the type 7 gradient, you can do all the rest. So implementing this is seen as a long term good thing, because we can support more PDF features AND it gives you a way of doing all the other more limited types of gradients (such as path gradients provided by GDI+ or Conical gradients which are handy for quick and dirty shading).

What I did NOT know was that there are people out there that go to inane lengths to draw hyper realistic things with mesh gradients. Take a look at this picture. That's not a bit mapped picture originally. It's rasterized from a vector graphic, using mesh gradients. You can see where they put some of the mesh lines in the lower right corner.