I recently tested out the zoom save functionality in Microsoft Outlook 2013, and it hasn't changed since Outlook 2010/2007. The zoom still does not save - you have to save the zoom everytime you open an email. This is true while reading an email in the reading pane or in it's own window.
We updated ZoomIn to work with Outlook 2013. ZoomIn works with 32 and 64 bit versions of Outlook 2013 (Note: This refers to bit version of Outlook and not Windows 32bit or 64bit. You can read more about how tell which version of Outlook 2013 you are running in our blog.
You can find the latest version of ZoomIn on our website at: http://www.sagelamp.com/Pages/ZoomIn.aspx