What network effects? Its just as easy to share files with someone who has Google Drive as it is Dropbox. In fact probably easier with Google Drive because more people have a Google account (800M ACTIVE gmail users was the last number I read).

As for switching costs, its pretty easy right? Drag from one folder to another?

Delta sync is a real issue, but what do you mean their mobile app pushes you to Google+, havent seen that....