Currently I’m thinking about moving from Evernote to Google Drive for most of my notes, because I want to consolidate most of my Web-Services.. And I find myself using Evernote not as much as I once intended..

The lack of tags is really bothersome, but I thought about an alternative way for Google Drive:
Why not just create folders and think of them as tags? You can assign files/documents to more than one folder in GDrive (much like labels in GMail).. This way you could assign “tags” to your documents.
How to select more than one folder:
Select the file, hit more -> organize … and select the folders you want the file to be assigned to with holding CTRL and clicking the folders.

And you could always create a “top folder” named “Tags” and all the “tags” are sub-folders of this one.. This way it won’t get messy.