I’ve patched the current version of TweetDeck to now include a logout button. Clicking on this button clears the local area where the username and password are securely stored and closes TweetDeck. When you next open TweetDeck you will be presented with the login screen. This is a somewhat convoluted and temporary measure for swapping Twitter accounts which will be replaced with a real account based solution in the multi-account version of TweetDeck, coming soon.
Also I’ve adjusted the tooltips which pop up over each button so they appear immediately instead of after a short pause. This should make it more obvious what each icon represents.