I've came across one of those magazine inserts that turn up every now again. You now the kind: half the articles are about things that no sane person would ever want to do, like create pink and green clouds. They get put on one side "for later review" and never see the light of day again until just before they hit the recycle bin. 
This one came out of What Digital Camera? - heaven knows when - entitled Photoshop Skills. Anyway, I thought "I'll have a mooch through - see if there's anything I can pinch". It gave me the idea of listing useful keyboard shortcuts. On the whole, I'm not a big user of kb 'cuts. I mean, I know it's supposed to be good to help avoid RSI from overuse of the mouse, but using the keyboard usually means two hands and I like to rest my chin in one hand and mouse around with the other whilst gazing reflectively at the screen.
So this isn't going to be an exhaustive list - there's probably one of those buried somewhere in the Adobe documentation (although there's no entry for keyboard in the help file) - but I'll include those shortcuts that I have found useful and do use regularly. and I'll make a special effort to extend this repertoire.
Copyright symbol: often asked and the answer is often
Space=Hand: Whatever the current tool is selected, if you press and hold the
Opacity Adjustment: Pressing one of the number keys will adjust the opacity of the currently selected tool, like the brush, or layer. Each key value is multiplied by 10, so 5 gives 50%, 1 sets 10% and so on. If both an appropriate tool and a layer are selected, the tool opacity is adjusted. If you press two keys in rapid succession, then opacity is set to that percentage value.
Alt-Reset: if you're working in a dialogue box setting the values for a command and you want to start again, rather than exit and re-open, holding the
Tab to Hide: Pressing the
F for the fuller figure: Pressing