My favorite feature in Google Docs is a little checkbox found in the Word Count pop-up. Check it and your running word count appears to the left of your doc. This is great when I have an assigned length and I’m not sure what I have left to work with. The only catch I’ve seen with this is that it has a maximum word count, after which it no longer works. So with my novels I can’t use it though the regular pop-up count still works.