your question inspired me. I have just written a little blog post on this topic: http://communities.ptc.com/blogs/hello_cad/2011/01/12/mapkeys
Maybe this is useful for you, too!
I have mentioned most of this in this forum in the past, but here again:
1. You are not limited to the letters of the alphabet and the F-keys; you can use number keys and special character keys as well.
2. It is most efficient to use one-letter mapkeys for your most frequently used tasks, but not for all mapkeys, because you may "use up" the keyboard. Therefore, a good idea is a judicious mixture of one and two-letter mapkeys. Two is plenty because "the keyboard squared" is more than you will ever need.
3. Two letter mapkeys are quickest if they are the same key twice, AA for example, or immediately adjacent keys, QW for example.
4. If you are using two-letter mapkeys you cannot also have one-letter mapkeys beginning with the same letters. If, for example, you have "A" and "AS", you will never see "AS" because "A" will execute immediately.
5. Consider using the single keys in the lower outside corners of the keyboard for quick access. (For example, I use the Z-key for Regenerate and the "." on the number pad for Save-and-Delete-Old-Versions.)
Most of our mapkeys are two-key.
Here are some of them, to give you some ideas:
F1: print to PDF (for release)
F3: print on A3
F4: print on A4
F12: print full size
cd: Change working Directory
rp: Revolve cut, use Previous sketching references (this drops you straight into sketcher, ready to create the next cut on a turned component)
ee: display Edges on/off (speeds up graphics with large assemblies)
zr: Zoom Refit
ii: Insert mode, Activate
rs: Regen Sheet (Update Current Sheet)
ro: Relate to Object
rv: Relate to View
cv: Copy, Paste Special (like Ctrl-C, Ctrl-V)