Google made some more changes to Gmail's labeling toolkit; all of following changes mean the end of Right-side Labels, an experimental Gmail Labs feature:

-You can now drag & drop messages into labels, just like you can with folders, and as "Move to". You can drag labels onto messages too. It's the same thing as using the "Label" button. To label or move many messages at once, first select the messages and then drag and drop the label. It's also possible to drag labels into the "more" menu to hide them and vice versa.
-Labels got new location on the left of your inbox or on the right, for those of you using the Arabic, Hebrew, or Urdu versions of Gmail.
- You can show, hide, or delete a label by clicking the down-arrow to the left of that label.