The ability to collaborate on folders can now be found within the main sharing flow. If you want to give friends and colleagues permission to upload to a folder in your Pogoplug account, select the "Share" option next a folder and then click the "Options" link.
Then simply check the "Allow Uploads" box. The users you share with will be able to upload files to this folder the same way they could previously with the "Collaborate" feature:
For more information on our updated sharing flow please check out our blog: http://blog.pogoplug.com/improved-file-sharing-2282/