Since OS X 10.6, when you’re screen sharing and looking at a remote Mac’s screen, you cannot successfully use Command-Tab to switch out of a screen sharing window, because the command is sent to the remote machine instead.

I recently found a way around this by using Quicksilver. With Quicksilver installed, the key combination is not sent to the remote machine, but rather to your local Mac instead—once you’ve summoned Quicksilver. When the Quicksilver window shows up, focus goes to local machine, and Command-Tab is also sent to the local machine.

Lex adds: And that’s just the tip of the iceberg. In his testing, my colleague Dan Moren found the same behavior works with Alfred; he could trigger Alfred’s shortcut while screen sharing, and the app would launch on his local Mac, and thus Command-Tab would begin working on the local Mac instead.

I’m a LaunchBar guy, though, and when I tried to trigger LaunchBar on my Mac—which I’ve set to use …

Source: Mac OSX Hints