Unhinged Scientist's Lab: what does lava destroy?
Channel: Eric Haines
Date: 2011-03-28

What does lava destroy? If you don't feel like seeing the experiments, the answer is: it'll flow over and destroy wheat, flowers, mushrooms, levers, torches (both kinds), redstone wire, and rails. Note it doesn't flow over plates, fences, or even wood or wool blocks. The only thing lava will eventually set on fire is wood logs, planks, bookshelves, TNT, foliage, and wool; with 1.6, wood stairs and fenceposts also are destroyed, though I haven't tested to be sure. It will ignite these blocks if they're above the lava, 3 meters or less away. It won't ignite wood steps or half-blocks, etc. It won't melt snow.

Some updated pictures:
Bookshelves do eventually catch on fire: http://bit.ly/hu6SWI
If you put wool blocks above a "shielded" lava block, the wool will catch fire (2 images): http://bit.ly/gqQlNJ
Lava does eventually set TNT on fire: http://bit.ly/hZc4Qv

A very cool result from this video http://www.youtube.com/watch?v=3Fj1O75Y9bI - you can put two wooden half-blocks together to make a wood block that does not catch on fire. I don't know if this still works in 1.6.

All things Vokselia at http://vokselia.com