I've been using Ubuntu Linux as my operating system of choice since 2004, and upgraded to the newest version (technically the release candidate) yesterday, also known as "the Hardy Heron". The proper release is today, and if you've never used Linux, I hope you give it a try. It isn't a radical improvement over the last version; it isn't meant to be, but be stable and robust.
One added feature, called Wubi, is how Windows user can try Ubuntu Linux without committing to it:
There is a new installation option for Windows users. Wubi allows users to install and uninstall Ubuntu like any other Windows application. It does not require a dedicated partition, nor does it affect the existing bootloader, yet users can experience a dual-boot setup almost identical to a full installation. Wubi works with a physical CD or in stand-alone mode, by downloading an appropriate ISO to install from. It can be found on the root of the CD as Wubi.exe. A full installation within a dedicated partition is still recommended, but Wubi is a great way to try Ubuntu for a few days and weeks before committing dedicated disk resources.
That alone is worth a look. (Let me see if I can find someone who's translated that quotation into Non_Geek.)
For details about the improvements since the last version, click here.