Google may be late to the party with Drive, it may even be last, but it's trying to present the service as something different from what Dropbox, SkyDrive, Box, iCloud and everyone else is offering.
On the face of it, that's not really true, you get a desktop app, cloud sync, mobile apps, a web interface and so on, standard stuff.
Sure, you can view some files online, without having to download them, but Google is not the only one offering that and, besides, that's just the Docs tie in.
But something that Sundar Pichai, head of Chrome and Apps, where Drive resides as well, Google Drive is not about the files it's about the apps, said is truer than it sounds,
Most people may use it and other similar services for the files they have on their computers but, as web apps become more common and more powerful, Drive will become a repository for files created and used exclusively online.
Drive is not quite there yet, but it's probably the one ahead of the pack. WIth Google Docs, already documents, drawings, presentations, spreadsheets are created in the cloud and live in the cloud.
But Google has opened up its API to allow other web apps to use Drive as their storage location. You can create or edit an image in Aviary for example and save it in Google Drive. Increasingly, more web apps will start using Drive, or other services that will offer the same functionality for this.
It's not just drive that does this, the best other example is probably Box which has a very solid platform. Dropbox has a very powerful and popular API as well. Microsoft has just announced a SkyDrive API as well.