The 3D slice lighting algorithm, while not viable now, will be soon, as we start to see next-generation cards having support for 3D textures in real time. A smart engine developer designs ahead of schedule. For those of you who don't know, OIM is basically doing diffuse lighting on a per-pixel basis. Because OpenGL doesn't support signed textures, you fake it by performing six passes, one which darkens, one which adds. Then you blop on an ambient pass and your texture, and wham.
Shadows are a more complex topic.
The distinction between shadows and lighting is important. At this point, there isn't really a good answer. The Radeon purports to have hardware accelerated shadows, which is very cool if ture, but I can't think of a good algorithm. I'm still working on this one as I'm starting to design the 3D engine for my current project. Anybody have any thoughts, send 'em my way.