I'm not a Microsoftie or fan, but while many of your points are very valid, helpful, and true, the ubiquitous 'Quit using Microsoft' is not really a solution.
First, in the business world, many companies use Microsoft products pretty exclusively. It's just what is accepted. Is it the best? No, but it is the most widespread.
That may not be an issue to you, in which case, go for it with Linux or Solaris or Mac or whatever.
But also, MS is attacked by these scumbag virus writers et al *because* it's a big target. If everyone switched to Linux, that wouldn't solve the problem, the scumbags would focus their attentions on whatever gets the most press and most audience.
I run MS products pretty much exclusively, and have never had a problem with a virus or spyware. I do of course use your 2, 3, 4 points, which EVERYONE needs to do [although I would require anti-virus, not just mark it 'possibly.']
I do use an alternate browser at home--I didn't like Opera that much. Mozilla Firebird. I pretty much use it just to read my comics pages ['Open All in Tabs' is a very neat feature.]
I would actually summarize all your points in saying, 'Educate yourself.' Both to the benefits/disadvantages of various software providers, and to the prevalence of Internet dangers, and to how to protect yourself from them. If that decision leads you to drop MS and go with another software provider, which works for you, then that's great.