Having not used Google Docs, I can't compare - but I will say this is really helpful for my company.
We have a Business Account, and therefore a ton of storage, so we archive all photos and videos to the cloud and not our computers. Marketing can ask Artistic to view a particular folder of images and they can comment on the side bar (of comments) about approvals, edits they want made, etc. Then Marketing gets a notification when comments are made. I've gone through and ID'd the artists in the comment area. A lot faster than someone writing down photo ID numbers and relaying them through email.
I can't wait to use it more!