What about when someone hacks your computer, and then uses it as part of a DDoS (distributed denial of service)? Security fixes aren't just for your benefit.

I think a reformat & reinstall takes care of that, I do it every few months anyway. Quick and painless, I don't have to worry about fixing my broken windows or worry about being "up to date" or worry about being hacked.

It's likely that it's from the compromised PC of someone with exactly that attitude, that I've been receiving an identical virus email every ten minutes for the past day and a half. Should I just wait a "few months" until this user reinstalls their PC, and hope that next time it's infected I'm not on the list?

Presumably you have no files on that PC that it would concern you to have (a) deleted or (b) emailed to a random address harvested from Usenet?

I don't administer a network of any kind

Oh, I see, you mean some other person has connected your computer to the Internet without your knowledge?

You at least administer the connection between your PC and the Internet; it's a network you can choose to administer irresponsibly or responsibly. If you choose not to administer it at all, you always have the option of unplugging it.

Peter