Dumping Charcoal in my Garden

The attempt to recreate the "terra preta" super soil found in the amazon is an interesting subject.
I usually toss the fines left over in the bottom of the bag from my lump charcoal into the garden and have no idea if
it makes any difference.

Here are a couple of other sources on Biochar.

Gardening with Biochar FAQ
Financial Times Biochar article