Previously, your free space from Google was segmented and ring-fenced between their various services, but that is all changing as you will be given 15gb to do what you want with. So instead of having 10 GB for Gmail and another 5 GB for Drive and Google+ Photos, you'll now get 15 GB of unified storage for free to use as you like between Drive, Gmail, and Google+ Photos.
Google are also making changes to the paid storage tiering by removing the 25gb for $2.49/month option with 100gb for $4.99/month now being the cheapest available.
Head over to the Google Drive blog for a full rundown of the changes.
[Via: Google Drive Blog]