You can use the ChunkWorx plugin for generating ahead; I think it's already part of the default install.
I just had one of those lightbulb moments, when I realized it's really really simple to produce caves without the single-block holes in their floors - simply chop off the bottom (and top) 20 % of the cave. Seems to work like a charm - check out rev 1296.
gonna try it now

does it have any effect on the speed of the generation?
well something realy changed ;P i've got an image of a place. one before[
attachment=252] the new caves and one after[
attachment=253]. the caves seems to be allot bigger for a reason.
Yes, they are bigger, because the small caves really didn't work well, I just didn't expect them to get this big. I guess I'll tweak the radius distribution function.
Ok, re-tweaked in rev 1298, this time I think the caves are really neat.
The recent speedup in biome generator has had its drawback, which I noticed only now
![[Image: bad_biome_optimization.png]](http://mc-server.xoft.cz/img/bad_biome_optimization.png)
I'll try to fix that while retaining at least some of the speedup.
Fixed. I'm quite amazed that the performance didn't drop much.
Finally I have a proper use-case for the cCuboid class. No longer do I want it removed (
https://forum.cuberite.org/showthread.php?tid=814 ), but I'm actually extending it. Why? Because the MineShafts structure generator will make extensive use of it

It's going pretty well; corridors are already working nicely, they're still missing some minor embellishments, such as torches, spiderwebs, tracks and hanging blocks, but generally they're okay.
I think I'll try adding some more variety now - the crossings.
One thing troubles me though, our height generator makes the ocean floor really low, sometimes as low as Y=14. That makes a lot of mineshafts carve through water. That will need some fixing, too.