This is a start to a new wiki to address the specific use case of MongoDB session cache being used on a website that is partially SSL encrypted. This will talk about the module Securepages being used with MongoDB and some of the problems that will be encounter.
Mixed Mode Switching
Mixed mode switching on a website is when you switch between encrypted and non-encrypted pages in the same site. There are arguments both for an against this. Google wrote a white paper on the SSL encryption of Gmail when that service launched years ago. Adam Langley of Google Security Team has written many blogs and posting around the internet about the true impact of SSL on the server/network. You can find his personal blog here.
The switching between SSL to Non-SSL has some implications with MongoDB session cache. Within this module, Drupal looks for the variable $account->uid to be populated. However with the mixed cookie session it is not available upon the start of the page generation where MongoDB lives an works.