If you click on your username in the top right corner of your my.pogoplug.com site, then click settings, you may add an email address to an existing Pogoplug account. Simple click "add email," and enter your friend's email.
If he/she is already registered as a Pogoplug user, you must input their password. Click Ok, and your two Pogoplug accounts should be merged.
However, allow me to let you know that if the email being added has entered into our billing flow after having purchased an upgraded account (Pogoplug Family or Team), this merging will not work. The good news is that if one has already upgraded their service, they may simple add users to folders within their account. This option is actually preferable for many of our customers because it allows them to selectively open folders up to access by another email, rather than merging their entire accounts.
Finally, let me warn you that if you add an email to your Pogoplug through the settings option (without Family or Team), the entire contents of your Pogoplug-attached hard drive will be shared, so make sure that this is what you want before proceeding.
Did this answer your question? If you have any further concerns regarding the security of your files when sharing or merging accounts, I recommend contacting support. They should be able to offer the answers that you need.