I use it for "simple" stuff - for instance, it's very convenient to have a place to take notes at meetings (I do a lot of that with my job). Since I always have wifi where I work it's just a matter of opening up the Drive website and creating a new document. And then everything's in one place and it's easy to find stuff with Google's search, which works on document names and document contents.
I do create some "production quality" documents from within the Docs world, and export them to PDF or DOCX so I can share. But these documents are generally simple; the complex stuff I do in LaTeX. I really do not like Word with its seven thousand ways to frustrate me and the weird layout that I've never really gotten used to since they majorly changed it years ago. Libreoffice and Google's docs editor are nice and relatively simple and I find them easier to use. But I go back to Word when I have to which is frequently since "everyone" seems to use it.
It's convenient to have the ability to open attachments (from Gmail) in Drive/docs for quick viewing, but stuff created in Microsoft's Office doesn't always convert very well.
I fully realize what Google is doing by "sucking me in" to their world and having everything I do be stored on their servers. Ever since I bought a Chromebook Pixel and got the 1 TB of Drive space, I'm always finding ways to use it. I know they just want to harvest everything I do - so for the sensitive stuff I have an encrypted (ecryptfs) partition with Dropbox that I can mount on my Linux machines, and for wholesale archival storage of sensitive stuff I use PGP and stick it wherever. If Google Drive allowed the ability to mount the drive partition under Linux like Dropbox does, I would probably "drop the box" altogether.