"Drive is built to work seamlessly with your overall Google experience. You can attach photos from Drive to posts in Google+, and soon you’ll be able to attach stuff from Drive directly to emails in Gmail. Drive is also an open platform, so we’re working with many third-party developers so you can do things like send faxes, edit videos and create website mockups directly from Drive. To install these apps, visit the Chrome Web Store—and look out for even more useful apps in the future."
Specifically the app integration ecosystem they're creating with the Chrome Web Store is extremely interesting. There's documentation for developers here:
https://developers.google.com/drive/
Basically, you register your app against certain mime types, and then when users install your app into Chrome, they can now open those file types directly from Drive using your app, seamlessly.
It's Windows' "open with" dialogue, except on the Web. That's a big deal, because while everyone expected Drive to offer features that compete with Dropbox, this feature competes with operating systems. I think it's a brilliant move that shows Google thinking ahead and beyond what Dropbox is doing.