I agree; the word fanboy should be treated as a personal insult.
And you're right, it's also used inappropriately. It's not uncommon for someone with a legitimate claim to be labeled as a fanboy, just because someone else disagrees with their opinion. Granted, there are some cases where the fanboy label is probably quite apt, but rather than calling them a name, they should simply be ignored (and reported, if applicable).
If someone is making a counterfactual argument, then that argument should be responded to with a factual argument. The flaws in the poorly-reasoned argument should be pointed out. Calling someone a "fanboy" is an argument substitute. The person using the term probably doesn't even know why they disagree, they just do.
See, what I think you guys are missing... and in most cases it is because you are coming from a platform that was never in any danger of disappearing, is the fact that the biggest danger to a minority platform is apathy on the part of the users.
I wonder how many people here remember EvangeList? Or MacMarines?