Canonical has published Ubuntu 9.10 (Karmic Koala), you can download it over here. The latest release of Ubuntu is based on Linux kernel 2.6.31 and GNOME 2.28, it features a redesigned, faster boot and login experience, a revamped audio framework, improved 3G broadband connectivity, and lots of other improvements. Full full changelog can be viewed over here.
Furthermore, the innovative '100 Paper Cuts' initiative organised with the Ubuntu Community allowed users to nominate minor annoyances that impacted their enjoyment of the platform. So far over 50 fixes have been committed, removing minor irritants such as inconsistent naming or poorly organised application choices. Larger scale user experience improvements include a refreshed Ubuntu Software Center, giving users better and more easily understood information about the software they have available - bringing the world of open source applications closer to the user. These improvements, in combination, have a transformative effect on the user experience.
Ubuntu 9.10 also includes the integration of 'Ubuntu One' as a standard component of the desktop. Ubuntu One is an umbrella name for an exciting suite of online services, which were released in beta in May 2009. Ubuntu One provides an enhanced desktop experience, simplifies backup, synchronisation, and sharing of files with an expanded set of features including Tomboy Notes and contacts synchronisation.
Ubuntu 9.10 also welcomes a host of features that make it the best platform for developers, whether professional or casual. Developers interested in writing applications that run on Ubuntu now have a simplified toolset called 'Quickly' which makes it fun and easy by automating many of the mundane tasks involved in programming. Quickly also helps users 'package' the code and distribute it through the Ubuntu software repositories. Ubuntu developers will now find all code hosted in the Bazaar version control system, which is part of the fully open source Launchpad collaboration website. It's never been easier to develop on or for Ubuntu.
There's also a new Netbook Remix of Ubuntu, that version features optimizations to run more smoothly on netbooks with limited computing power and small displays.