i would love to be making my own, but i cannot tolerate smokes of any kind. what little i get comes from charcoal chunks in ashes that some friends bring to me. it really isn't biochar as i'd want it to be but better than nothing... i think it can be helpful for some soils, but like any amendment it should be used with care/thought. a straight application to a garden is likely to be trouble if it isn't innoculated first (i've read of people who put it in their compost piles first which seems common sense to me - i've put a little charcoal through my worm bins to innoculate it and that went ok from what i could tell, but it wasn't much). considering that it will last a fairly long time and has such a huge surface area for bacteria, fungi and other soil creatures it seems like a pretty good thing, but then again, if you are in an area that is already pretty hot then adding something to the soil which makes it darker may be an issue unless you keep the soil very well covered with growth or mulches...
Have you seen this video? It is a method of making biochar inside a wood stove, as you are heating your home. I make at least 2 small batches a day, burning wood chips, tree clippings, twigs, floor sweepings, and even old bones the dogs won't bother with anymore. Works great. I run the charcoal through an old food processor to powder it, then add to my compost pile. I've been doing that for a year now, but my first compost pile isn't ready yet, so I can't say how it is affecting my soil. But I can imagine I'm at least sequestering some carbon....
Kathy Dawson from Manjimup is a local expert and proponent of using biochar. You could try contact her for more info.
We use it in combination with wood mulch and more "traditional" effluent from solid animal waste for the creation of highly enriched soil. In the more complex systems such as the food forests, it is almost a redundancy, but for some of the monocultural (or almost monocultural) agricultural growth, it serves its purpose very well ... also great for foot farming and the elevated or vertical farming methods.