The key differentiator for Google Drive would be online interfaces. I love Dropbox to death, but the fact that when I am on a strange computer I have to download a spreadsheet to make a minor edit and then upload again is completely annoying. And it is mostly useless for media playing. If Google gives me a box to store/sync stuff offline and makes Google Docs/Music/Picasa seamlessly work with that box, I'd switch in a heartbeat.
On the other hand, Dropbox's integration into the native OS is one of their best selling points. If I remember correctly, they actually had to do something along the lines of code injection into Mac OSX's Finder in order to get the dropbox-centric icons and options to appear[1].
Box.net only offers desktop sync to larger clients, and other competitors have yet to beat the frictionless Dropbox experience on native computers.
The way Google could win would be auto-import from Dropbox, tight OS integration, and online editing in Docs.
box.net offers a webdav interface, even for their free accounts. That's an open standardized interface for box.net vs. a proprietary client for Dropbox.
True, but WebDAV clients are nowhere near the perfect user experience that the proprietary Dropbox client provides (at least on OS X and Linux, I don’t know about Windows).
