Google Docs is awesome. It allows you to share and collaborate in real time. It automatically saves every change you have ever made, so work is NEVER lost. It allows you to access your docs no matter where you are!
There's really no downside. Unless you are an idiot like me.
In that case, you might accidentally name your final draft the same name that you gave your very first draft. Then you might "Share" a draft with that name with your agent, only to realize and go into a panic because you think she is reading your first very rough, choppy, sloppy, disastrous mess.
And then you might have a complete freak out and make it worse by writing to her to try to explain it, when it fact, you actually sent her the correct final draft all along.
So, if you don't want your agent to think you are a lunatic, it might be better to avoid Google Docs altogether.