I use Google Drive as a common drive between all of my devices.  It works out pretty well.  If I were to draw something on my iPad, I can save that out to my Google Drive.  By the time I get back to my computer, the PSD is already sitting there waiting for me.

I run into a major challenge when working in Photoshop on the Windows machine.  If I save my work too often, I get an error telling  me something about needing administrator access to save the file to Google Drive.  I end up having to save the file to my desktop, then moving the file to Google Drive when I finish.  This is one of the small things that happen that make me prefer Mac over Windows.