I love Google Docs! It's where we store tons of information in the lab–it is essentially indestructible, easy to use and easy to share. And, perhaps most important of all, it makes collaborating on documents SO much easier. No more endlessly sending around XYZ_manuscript_final3_actuallyfinal8.docx. The Word Doc sharing method is prone to errors and is slow, especially if you have many collaborators.
However, the one feature Google Docs was missing from Word was the infamous "track changes". Warts and all, this is an essential feature, since it allows editing while also showing you directly where the edits happened. Google Docs had great commenting features and had some version history feature, but it just was not as good as good-old track changes in Word, end of story. But now it exists! It's called editing in "suggest" mode, and you can change modes with the little pop-up menu towards the top right corner (it's in "edit" mode by default). So awesome! Now witness the firepower of this fully armed and operational Word replacement!