I was fighting with exactly the same question just a few days ago, but I extended it yet about Dropbox, Drive and similar services.
From Google products, I use GMail (my main account), Analytics, Docs, Drive, Google Apps, Youtube, which can be scary, on the other hand, I don't store there any illegal kind of information or stuff that could be flagged/deleted.
I ended up with accepting that Google does scan everything what I do on the internet, but the same does for example Facebook (and Microsoft's Windows as well).
I don't really think that using Microsoft Office 365 changes something.