My account was made active just a short while ago, so I decided to install the application. From what I can see, the application itself appears to work just like Dropbox in that it creates a "Google Drive" folder and anything placed in here is synced online, with a green tick mark on each file that successfully sync'd.
The one problem I have with Dropbox is that at work we use Dropbox to sync files with work colleagues on the move. What this means is that I can't install a separate Dropbox for myself as only one Dropbox account can be configured with a specific PC. However, as Google Drive can be installed on a computer already running Dropbox, this gets around the issue, so I can use Dropbox for work stuff and Google Drive to sync my own stuff.
One feature I do notice missing is the ability to quickly restore a previous version. E.g. with Dropbox, I just right-click a file, select "Dropbox" and "View previous versions", where as Google Drive files do not have this right-click option, i.e. I need to go into the web interface, find the file in there and then view revisions. Although I haven't tested, I do wonder if revisions count towards the space usage, as Dropbox only counts the latest revision of every file against usage.