That would be "in before somebody says 'don't run Windows'".
Having said that, I've run Windows (among other things) for years, and haven't run anti-virus in over a decade for two reasons:
- it's more trouble than it's worth when you know what you're doing,
- it's hard to do any kind of virus research at all when you've got antivirus trying to delete every infected file you're examining.
In the time I've not run a/v, I've never had an infection. (I never had an infection before that, either, but that's beside the point.)
I use Comodo Endpoint Security on the kids' computer, and the HTPC, but my main Windows desktop hasn't had it for years, and won't have it for the foreseeable future, either.
All my Linux machines, of course, don't run anything, except for my mail server, which has ClamAV on it, just to scan attachments.