You can burn them, but it's really dangerous. It can get out of control pretty fast.
UPDATE: Shears should now be used to get rid of leaves. They're 6 times faster than using your bare hands (and 4 times faster than using a sword).
Alternatively, you can use a sword if you don't really care about damaging it:
Leaves can be destroyed faster by
using a sword, though swords lose
double normal durability when used on
leaves. As no other tool yields any
increase in removal speed, leaves are
best removed with bare hands, or a
block or object unaffected by
durability, so as not to damage your
tools unnecessarily.
Finally, as Jonathan mentionned, the leaves will decay after a certain time if it's not attached to solid blocks (but I don't consider this a 'quick' way to get rid of them):
In Beta, leaves decay according to a
simple formula: leaf blocks decay
unless they are within 4 blocks of a
log block, and connected to the log by
other leaf blocks. Thus, harvesting
the wood from a tree will cause the
leaf blocks to vanish randomly one by
one.
Update: According to Notch's blog post about changes coming in 1.6, the torches-on-fast-leaves bug is getting fixed:
- Fixed buttons and levers being placeable on leaves in “fast graphics” mode
This means that monsters can no longer spawn on leaves, either, as they are always considered transparent, even when using Fast graphics.
Monsters can spawn on any solid, non-transparent block which is at light level 7 or lower.
Signs, torches, rails, and the like are ignored when spawning monsters; they'll spawn on the block underneath just fine. This is why one-block-wide railways need to be lit.
Transparency means whether or not light passes through a block rather than whether you can see through it. Half-blocks, doors, stairs, and glass all count as transparent and prevent monster spawning. Leaves, oddly, count as transparent only when Fancy graphics are enabled. An easy way to test a block for transparency is to try placing a torch or sign on it — neither can be placed on transparent blocks. (Meaning that torches can be placed on leaves with Fast graphics, but not with Fancy.)
Torches put out light level 14, so monsters can't spawn within 5 blocks of a torch orthogonally or 3 blocks diagonally. If you put your torches in a diamond pattern, they can be up to 9 blocks apart, but it's best to move them closer than that on uneven terrain. (I use 5 myself.)
If you like, you can actually torch your treetops by changing your graphics to Fast, placing the torches, and switching back. Your torches will stay rooted, even though you wouldn't normally be able to place them that way. Personally, I think it makes them look rather cheerful. :-)
Best Answer
How can you get more coal?
You are running out of fuel?
You are running out of trees?
Charcoal is very slightly different from Coal. It cannot be used for crafting the upcoming coal block, and does not stack with coal.