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Pro 15GB free
This space is shared across Drive, Gmail & Picasa.
Pro Integrates with other Google services
For example, you can use search to search through both Drive and Gmail.
Pro File sharing & collaborative editing
Google account holders and non-holders can be set to access and/or collaborate on files/folders in real-time. Additionally, you can find files you've shared not only by filename but by person you've shared the files with.
Pro Extended functionality via apps
Pro Built-in office suite
Includes tools for writing, presentations and spreadsheets.
Pro Revision control
By clicking Ctrl + Alt + G in Windows or Command + Alt + Shift + G is OS X you can access previous version of the file.
Pro Save files to drive directly from Gmail
Drive lets you save any file from your email.
Pro Cheap for extra storage
$1.99 per 100GB, for up to 16TB.
Pro Mobile integration
You can work from any device, especially mobile.
Con No client for Linux
Google as of yet has a client for Linux, leaving many who use the service forced to use third party apps or the webpage.
Con Very unreliable
Desktop client constantly crashes.