I just stumbled on this one. (Sometimes during a Beta period, you have to "find" new features yourself!) In the past, when you wanted to remove a Label from one or more messages, you would have to click on the desired Label on the left of the screen, select the message, and then click on the "Remove Label" button. Well, The process has been significantly simplified! Read on for details...
While viewing a message, click on the "More Actions" dropdown, scroll to the bottom of the list, and select the desired Label to remove. Voila...the Label is removed!
If you are viewing a list of messages (say, in your inbox or in a Label view, click the checkboxes of the Labeled messages, click on the "More Actions" dropdown, scroll to the bottom of the list, and select the desired Label to remove. Again, the Label is removed!
Don't forget that if the message has been Archived and you remove all Labels, it will be visible only in the "All Mail" view.