Not very conclusive but Nilay highlighted the fact that while Dropbox's terms seem friendlier, in legalese, it's perhaps has more leeway.Also, he mentions that Google's unified policy means that they have to be extra verbose/careful about this. For example, if I can attach large documents from my Google drive while e-mailing from my Gmail account (basically not have to upload it from the local system), I'll consider that to be an interesting value addition; but that'll require me to give Google the right to move files between their servers, maybe compress it etc. This is a hypothetical example.
I trust Google as much as I trust Dropbox (which is to say that I'm cautious) and I expect Google to refine their offering as well as their policy over time.