I would love to take a class on how to use Adobe Photoshop. Instead I learn this bohemoth of a program by trial and error, by scouring their Help program and by asking Mr. Google to show me how to do stuff.
Most recently, I discovered that you can load any sort of brushes. I'd heard people talk about brushes, but I didn't understand their useage until recently. So coupled with my ability to download copious amounts of free fonts, I have been working on some graphic work for my band.
Obviously still have a lot to learn, but it's so addicting.