Good ideas about the shortcut keys, I'll submit some suggestions about this to R&D.
The * key on the numeric keyboard will toggle between TopLayer, internal layers and BottomLayer. It skips internal planes. If you are on the other layers after BottomLayer, then it's easy to get to the TopLayer by pressing * once, so I find that a useful "home" key, used with the +- keys that keep cyling through all of the layers.
The same keys function while routing, which is obvious, but I point it out because some people don't realise it. The track color changes and the large color square (with LS next to it) also changes, so you can see that out of the corner of your eye to know that you're on the correct layer before placing the next track segment. This is especially useful if you're routing to a midlayer.
Best regards,
James Harriman
Altium