iPhone, iPod, iPad
Depending on your device, there are certain functionality restrictions. If you play on an iPad, you have a search function on both your gifting screens and your material requests screens. On the iPhone or iPod you do not. This makes selecting your "active" friends to gift or request materials from much more difficult.
No idea when or if Playdom will correct this to ensure uniform functionality across the devices.
Some iPhone/iPod users have also reported they are completely and totally unable to receive gifted energy. Complaints to Playdom abound, but this still remains an issue. Deleting & re-installing the game MAY repair this issue, but you'll have to backup to facebook first.
Some iPhone/iPod users also lack the trophy, for global "Like" rankings, and neighbour comparisons.
Some iPhone/iPod users do NOT have the login screen for Facebook.
TY to Rachelsplaceofstuff and Invictus for bringing this to light. See Rachel's comprehensive list of game variablity here.