Hacked in some trees to test with:
(Yeah yeah, trees are growing on the beach, I know. This will be much better once biomes are implemented.)
The shadows look nice, but I wonder if it would look more natural with some sort of volume ray casting algorithm. This would not be hard to implement; instead of simply checking whether a ray intersects a block, you assign a transparency to every block type, and calculate how much light is left after it passes through every block that intersects the ray. But it would slow down the light map generation even more.
Also, I noticed something odd while looking around:
The far trees overlap the nearby tree. Hmm, I thought one of the reasons to use a 3-D engine is that you don't have to worry about z-ordering and all that low-level stuff? I'm sure this is just me being a n00b with Irrlicht, and there's an easy and obvious fix for it...