Canonical has just released Ubuntu Linux 11.10 (Oneiric Ocelot) on 14 October 2011. You can freely download and install it from here.
In this version, we can see major upgrade to its Unity user interface, with refined Dash and improved Launcher and Filter. The Ubuntu Software Center is now looks even more alike the Macintosh App Store.
It has replaced Evolution with Thunderbird as its default email client.
It has tighter integration with the Ubuntu One cloud service.
The Linux kernel has been upgraded to version 3 too.
While Ubuntu 11.04 (Natty Narwhal) is a major revamp that brings in new user experience, I would say Ubuntu 11.10 (Oneiric Ocelot) is the subsequent refinement and stabilization release. The coming version of Ubuntu 12.04 (Precise Pangolin) will be a Long Term Support (LTS) release.