Sharing is clunkier, when you share a folder with somebody it doesn't appear in their drive. After they accept they still need to go into their options to get it to start syncing.
There are a lot of Apps that have Dropbox built in. They use Dropbox as their storage.
I feel Google isn't putting the effort into their Desktop client that Dropbox is. Google wants people to use the web. They are both cheap enough price isn't an option.
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....
I find Dropbox websharing far easier, right-click share and it puts the link on the clipboard. Google drive makes you go through a dialog.
Google Drive doesn't have history for non google doc files. We use it as a simple version control for all our documents.
Just about every time I start a new project with an outside client, one of the first things they do is ask to set up a Dropbox share for the project. I've once had a person want to use Box, and never had anybody even mention Google Drive.
I'll have to stick with Dropbox so I can sync across Windows/OSX/Linux, my phone, etc. Besides I get faster upload speed on Dropbox, so I can sync all my holiday photos.
Support: If Google suspends/deletes your account, you're pretty much done. Their interactive support is below the level that other companies commonly provide.
Risk: Google raised prices 3X+ for Google App Engine on short notice. They could do the same for Google Drive.
Dropbox works flawlessly for me (including w/ Linux) and doesn't have the issues above. In this case, you do get what you pay for.