An unbelievably helpful OS X setting
I've no idea why I didn't learn this until recently, but this seems to be a crucial setting for a enjoyable keyboard-centric use of a Mac: Full Keyboard Access.
After using this, many more OS X UI elements are navigable with just the tab key, and no mouse. This Apple support doc describes the keyboard shortcuts that it enables.
Hooray for less use of the mouse!
Thanks to Matt Gemmell for posting a great article that includes this tip and many more.