For three months now I have used Ubuntu as the operating system of choice replacing windows XP on my home computer.
For the most part the transition was quite easy and it's clear why people are begining to talk about it being able to replace windows for some users.
But there is of couse always a but - and this is a major one for me. Linux and Ubuntu in particular allows you to easily install programs that are compatible with your particular flavour - e.g. Adept installer, synaptic installer or command line utilities such as apt-get etc...
However one problem I have repeatedly come across is I install a program to find that it doesn't work