Well, there's some truth in this. My father, a US Forest Service officer, laid in lots of firewood (I carried much of it while growing up), and one night we did in fact have a chimney fire (we lived in a double-wide mobile home with a nice stand-alone wood stove). Rather than call the local city fire department, Dad went out and watched the flames shoot out of the chimney to see if anything else would happen. Our roof did not catch fire (he had a hose handy in case it had) and nothing else happened. After a while, the flames stopped. Dad decided that the fire had burnt the build-up off and done no other harm, and we never had any more troubles.

Lisa points out that this is well-seasoned pine, not newly-cut, and that helps keep the fire hot and thus reduces build up. Also, the wood stove insert we have here has a catalytic element that re-burns the smoke (as long you keep the fire hot enough), and that also reduces build-up.

I prefer a nice hot fire. In fact, I don't like seeing any smoke come out of the chimney at all. It should only smoke when you first start it or when you're loading fresh wood.

Steam locomotives are the same way, incidentally. Big bellowing clouds of smoke from the stack may be photogenic, but they're inefficient and much more polluting than a nice hot fire in the firebox. A railroad fireman who consistently generated lots of smoke would end up searching for new employment eventually. Steam exhaust you expect, but not lots of smoke on a well-maintained steam locomotive.