I use Apple’s built-in Screen Sharing app all the time to connect from my Macbook Air to my Mac Mini. It’s a great way to just quickly log in from the Air and restart a Minecraft server, for example, or get a screenshot of the latest OS X Mavericks beta feature.
I also use Command-Tab a lot on my Macbook Air to switch between running apps. However, I was never able to Command-Tab my way out of Screen Share, as the keyboard combination gets sent to the remote Mac Mini, keeping me fully in Screen Share Mode.
Until now.