I find there are two classes of Mac users: those who like to use the keyboard as much as possible (like me) and those who scoff at us, insisting that it’s more Mac-esque to just use the mouse. A big annoyance of mine since I’ve started using OS X more regularly has been the inability to tab to buttons in dialog boxes or to dropdown lists in web pages. Just now I discovered that you can toggle “full keyboard access” by pressing Ctrl+F7 (^F7 in Mac-speak). Try it out if you’re on OS X: go to a page which contains dropdown fields (e.g., http://www.digg.com/register) and notice that you cannot tab to the dropdown fields by default but you can after pressing Ctrl+F7. And when you get dialog boxes in Firefox (e.g., the Remember Password dialog), you can tab between the buttons. Hooray!
I also just discovered that you can hide windows by pressing Cmd+H. I’ve been pressing Cmd+M to minimize windows to get them out of my way but then I cannot use Cmd+Tab to get back to the application if I’ve minimized all its windows. Hiding windows gets them out of your face but easy to get back to by clicking the Dock icon or using Cmd+Tab. I’ve also become a big fan of Witch for switching between windows using Cmd+right arrow (Cmd+Tab switches between applications and then you have to use Cmd+` to switch between windows in that application – yuck).
Also, if you use Windows in a virtual machine on a MacBook (I’m trying out VMware Fusion right now), you might get frustrated that the function keys aren’t really function keys by default. So if you press Alt+F4 in the virtual machine, you turn down the sound instead of closing a window. You can go to the Keyboard & Mouse section in System Preferences (in OS X) to configure the F1-F12 keys as proper function keys. That means you will have to use the Fn key to control hardware settings like brightness and volume, so pick whichever mode will cause you less grief.