Rapid Start allows for systems to resume from deep sleep in about five seconds and is expected to perform better than traditional suspend-and-resume. Rapid Start is a combination of firmware support -- found on latest Intel motherboards namely for Ivy Bridge / Haswell -- and a special on-disk partition for storing the RAM contents.
Support for this Intel technology was merged into Linux 3.11, but it's still not clean and easy to setup for end-users nor are there any GUI controls for enabling/disabling Rapid Start or toying with other attributes. The Ubuntu Rapid Start session at today's virtual Ubuntu Developer Summit were basically about the matter of having support in the Ubuntu Installer for being able to identify systems supported by Rapid Start and having an easy way of controlling the feature.
With the feature freeze this week for Ubuntu 13.10, this is mostly work that would go towards enhancements in Ubuntu 14.04 LTS. For those wanting to find out more details on Ubuntu's plans for Rapid Start, the Google Hangout video is embedded below.