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Pro 15GB free
This space is shared across Drive, Gmail & Picasa.
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 Integrates with other Google services
For example, you can use search to search through both Drive and Gmail.
Pro Extended functionality via apps
Pro Built-in office suite
Includes tools for writing, presentations and spreadsheets.
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 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 Mobile integration
You can work from any device, especially mobile.
Con No official 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 No universal Windows app
Con Doesn't integrate well with OS
Con Very unreliable
Desktop client constantly crashes.