I have messed around with Ubuntu (not on my new machine yet) and it is super silky smooth... too bad we cannot run our games on it. As RR said... maybe someday.
I did want to recommend the solution for me which has been far better than any anti-virus software - Smoothwall Express firewall -
www.smoothwall.org - its open source so its FREE... and it is the BOMB for network protection. Sure there are other options... but SE is stable and solid with clear controls. Take an old PC and load it up... then be shocked at the number of daily intrusion attempts you get (I was). Have not had any kind of trojan or worm or malware issue since I started using Smoothwall. Do yourself a favor and check it out...