I still don't see any practical reason to use any third party anti-virus solution for Windows, at least at the desktop level, now that Microsoft Security Essentials is out there. It works very well for desktop installations and it simply removes the need for any other solution.
I wouldn't support MS-A/V at first. But their detection rate is good now and it causes less problems that most A/V packages.
I'm installing it now on most machines - except for older/slow systems. They get Panda Cloud (minus crap-ware) as it is lighter weight and behaves well enough. -- Adopting other people's animosity is The New Stupid.