Ubuntu is the most viable open source competitor against Windows and Mac OSX to date. Sure, 31337 #4XX0rZ might compile a Linux kernel from scratch or custom configure their own Debian system. A Ubuntu distribution offers a one-stop installation that can be later customized according to user preferences or used as is. Almost everything can be done through the graphical interface rather than through text commands. Ubuntu can be a non-intimidating graphical GUI for casual computer users or a robust Debian-based distribution for computer nerds.
If you're tired of Windows viruses, crashes, and slowdowns, try Ubuntu. It has the same look and feel of Windows, but is more resistant to buggy programs.