Trying to switch to an apple keyboard on Ubuntu 12.04 brings up a number of issues. There's lots of old information out there on google, I'm going to post this as the current solution.
1) On a regular keyboard, you're used to having alt next to the spacebar, and the silly Windows, "Command ⌘", or "Super" key sits unused between ctrl and alt. But apple puts their ⌘ key right next to the spacebar making the alt key you use all the time harder to thumb. Trying to fix that with xmodmap and .xinitrc has no effect outside of terminal applications.
2) alt-f2 to run commands doesn't work anymore? That was actually broken until 12.02, but should be fixed now. That stumps you until you realize:
3) that the f* keys across the top by default now do nifty/useless things like changing the volume of the music. There's a "fn" key where the useless "insert" key used to be that you have to hold to get them to do their normal behavior.
4) The naive approach of using Settings / Keyboard / Shortcuts / System has the "Show the run command prompt" Disabled and italicized, and you are unable to enable it
5) Some instructions on the web tell you to use ccsm, the "CompizConfigSettingsManager" under "Gnome Compatibility" and enable the "Run Dialog" but it stubbornly stays disabled:
6) The "PrintScr" key at F13 doesn't do anything, with or without the "fn" key.