Although Canonical have kept true to their twice yearly release schedule, one in April, one in October (thus the .04 and the .10 version numbers, you'll remember), upon downloading and installing this release, which has perhaps the most amusing title of any of the Ubuntu releases before it (yes, even Hoary Hedgehog!), you'll see that there isn't much that's new to 13.04. The main gain in 'Ringtail is the performance. The distribution feels faster in Ubuntu's Unity interface than it ever did before and a lot of work has gone into this particular area.
The rest of the features that arrived in this release are mainly cosmetic, or small tidyups - a bluetooth slider button here, a jazzy 'shutdown screen' there. There's some nice unification of search services and social options on a per-app basis, but all in all there's not much too it. This is polish, without the spit.
I can't help but think though that Canonical have deliberately kept this release a quiet release so that they can concentrate hard on making the upcoming LTS (long term support) release. Canonical will be feeling the pressure to have this a solid enterprise grade linux operating system, and from what it looks like, that's where their efforts are really going right now.
For example, look at all of the Ubuntu server enhancements going on at the same time - Juju, a system made up of 'charms' (oh how kitsch!), you can download a charm from Ubuntu's free 'charmstore' for Juju which rolls out best practice deployments of things like Mysql, PHP and Ruby on Rails or deploys Cloudstack or Amazon EC2 integration systems amongst many other things. The idea is that doing all of this is as simple as clicking a button.
They even offer it to be integrated into their new MAAS system. For those not in the know, MAAS is Canonical's Metal-as-a-Service offering. They give you a physical box in the cloud which you can deploy/dev apps onto in real time without any of the lag of shared virtual environments. Think of it as physical boxes in the cloud with all the simplicity of virtual deployment in the cloud.
Finally, don't forget that Ubuntu Touch is being heavily worked on by some of the senior folks at Ubuntu right now. Johno Bacon stipulated recently that Ubuntu Touch should be ready for prime-time with the release of 14.04 LTS so, like Apple before them, this will be diverting some of Canonical's overall attention from the desktop as they too venture into the unstoppable world of tablet and smartphone. Recent feedback comparing other open source touch based operating systems such as Firefox OS already state that Ubuntu Touch is more impressive than Firefox OS.