Ubuntu 8.04 wins eWEEK Labs Analyst's Choice Award and is deemed ready to take
on Windows.
Read the article here:
www.eweek.com/.../Ubuntu-804-Is-Ready-to-Take-On-Wi\
ndows/

My personal opinion is that Ubuntu or any other Linux distro will not offer a
serious challenge to Windows until it is pre-installed by OEMs and is widely
available on new machines because many new users can't install an OS of any
kind, but this is good news.