Yes, I heard that too. Earlier this year I used soot on my potato bed and I've had minimal slug damage. The soot is dumped by a cleaning firm behind the hut of my local horticultural society for everyone to help themselves. However, I've decided not to use it again because there is no way I can know what was burnt in the fires and what chemicals the soot may or may not contain...
I do use wood ashes (as a fertiliser and to raise the PH of thre soil slightly), but the ashes are from my own fire so I know exactly what it's made of!