As I see it: Dropbox innovated, and they innovated well. It's inevitable that competition would arise, but competition on the scale Google can offer could well mean total annihilation for Dropbox, if annihilation is what Google pursues.
Google doesn't "need" to enter this market. And yes, I know that there's no rule that says you have to be nice... but it feels crappy to me. Dropbox has earnt it's success, and Google could easily let them grow and secure their future before releasing G-Drive. Google is in a position to be something of a patriarch in the tech world as opposed to eating it's young.
If I was working on a Dropbox competitor yesterday, today I'd be finding something else to do. That's bad for innovation.
if G-Drive actually exists that is.