Pandora's Web-based client keeps a tab open in your Chrome window. Unfortunately, if you're one of those people who has a lot of tabs open, you may accidentally close the Pandora tab in the middle of a great song. You could easily re-open the tab, but you probably won't continue hearing the same track.
With the SoundControl extension you can control Pandora from the Chrome toolbar, and even hide the actual Pandora tab from your window. Here's how to get started: