The most interesting bits are at the bottom of the release page:

Linux Mint 17 will receive security updates until 2019.

Until 2016, future versions of Linux Mint will use the same package base as Linux Mint 17, making it trivial for people to upgrade.

Until 2016, the development team won't start working on a new base and will be fully focused on this one.

http://www.linuxmint.com/rel_qiana_cinnamon_whatsnew.php