The mycologists tell us exactly what it is:
"Baudoinia are cosmopolitan colonists of exposed surfaces subjected to large diurnal temperature shifts, episodic high relative humidity and wetting, and ambient airborne ethanol. Morphologically B. compniacensis resembles some anamorphic Mycosphaerellaceae in possessing dark brown, nonseptate or uniseptate conidia with coarsely roughened walls that are borne acropetally in unbranched chains and released by schizolytic dehiscence. Analysis of partial nuclear rDNA SSU sequences positions B. compniacensis in the order Capnodiales and reveals that it is most closely related to the microcolonial genus Friedmanniomyces."
Now that you know technically what it is, I'll tell you what it really is. It's that sooty-looking black gunk that coats the outside of homes, spreads over porch furniture, blankets car roofs, covers plants and lawn shrubs, and is ever-present and annoying everywhere in the world where whiskey and other alcoholic beverages are distilled, stored and/or bottled. It's been dubbed the "Whiskey Fungus".
Until 2007 when researchers published a scientific study no one really knew what it was, but everyone disliked it equally. The NY Times has done an expose on it now that there have been five class action law suits filed in Kentucky against the distillers in that region. By the way, the distillers are none too happy about it either.
Seems it is a very old fungus that germinates on ethanol when the temperature and moisture conditions are favorable - yes, it needs relatively moist (humid) conditions in the ambient air to really get going, but not all that much ethanol - just a few parts per million will do the trick. In fact, much of the problem it appears is the normal distillery process evaporation which is surprisingly low. So, if you have water in your air, you'd better keep the ethanol out of the area. You've been warned!
Now I'm wondering about my neighbor who drinks a bit and keeps his house too warm. Could those age spots he keeps complaining about be....? Nah! We're too dry for that!