I've been taking Applied Plant Pathology this semester, so when @anneheathen tweeted that her tree was "diseaaaaaaaased" it was great practice to try and help her out :) She posted some photos and a description of the "Dreaded Spots" on her maple trees, and I immediately recognized the culprit shudders Tar Spot.
We actually just discussed this unfortunate problem in class. Its caused by a fungus (Rhytisma) and doesn’t cause any long term health problems for the tree but its certainly ugly isn’t it? Here its shown on Norway Maples, which is one of the reasons I dislike this tree as a municipal street tree. The diseased leaves store the fungus over the winter and in the wet of the spring the spores that spread it are produced and carried to new trees where they begin the infection again. They don’t actually spread “the Dreaded Spots” by touching.. best way to control it is to rake up the gross leaves now and get them AWAY from your yard. To answer Anne's last question: LoL no its not Lupus!