It turns out that the upcoming Google Drive release will add support for third party apps and Google will also include a SDK for developers. This way, you'll be able to open the files stored in Google Drive using non-Google apps. The Google Docs source code mentions "SDK" several times in connection with Google Drive and the "open with" feature.
There's also an interesting message that suggests Google Drive will integrate even more with Gmail: "Say goodbye [to] email attachments and hello to real time collaboration. Drag anything shared with you to My Drive for easy access."
In a recent article, Wall Street Journal reported that GDrive "is expected to launch in the coming weeks or months and will be free for most consumers and businesses. Google will charge a fee to those who want to store a large amount of files."
Most likely, Google Drive is an important upgrade to Google Docs that will detach the online storage service from the Google Docs apps and will make it more useful by offering more free storage, syncing apps and integration with web apps developed by other companies.