I'm not quite sure if it is legal either.
It is a great alternative for people with very small HD's though.
And I do think it'll be kind of slow too... it's not that you can open the file right away. Say you rip a bought CD to MP3s to your computer, and you move it to your GDrive, you won't be able to listen to them, will you?
So I don't really think it's that good ...
Well yeah, you can store things, but still.