In reply to TheDrunkenBakers:
A lot of people do put it in their compost pile, it raises the ph so a little will counter the composts tendency towards acidity. if you dig it directly into soil which already has a high ph then you'll raise it to the detriment of most plants you might wish to grow. If you dig it into a low ph soil then it will be beneficial to a lot of plants. A lot of berries like slightly acidic soil though, as do potatoes I think, so you wouldn't want to put ash anywhere near them. But then potatoes like potassium and that's in ash. Some people make a slurry/ash tea, I'm not sure why. Perhaps it removes some things and leaves a concentration of others.
It depends on how much ash you have, what kind of things you compost, what ph your soil is and what plants you're growing. Just chucking it into the garden willy nilly as a way to dispose of it isn't necessarily going to help. I think there's more in there as well, nutrients and such which complicate it further. Mine all goes in the bin.