[ Before and after look of my Places menu. ]
The Places feature in Ubuntu is similar to the Favorites in Windows. The folders inside it appear in the Places dropdown on the Ubuntu taskbar, in the rightpane of Nautilus (the file manager) and in the right pane of any Open dialog of any Ubuntu application. I find the default folders in Places cluttered and useless. I have no use for the default folders (like Documents, Music, Pictures, Videos and Downloads) since my organization is different and is placed elsewhere. So, I like to remove most of the Default folders and add some frequently accessed folders (like Dropbox).
To remove a folder from Places: Open Nautilus. In the right pane of Places, right-click the folder you want to remove and choose Remove.
To add a folder to Places: Open Nautilus. Go to the folder that contains the folder you want to add to Places. Drag the folder you want to the right pane under Places.
All the folders added or removed are automatically refreshed to the Places taskbar menu and all Open dialogs.