We're going to have to agree to strongly disagree here... but a lot of it depends on what aspect of fanboyism irks you. I've seen them all.
1) Microsoft fanboys are pretty mild. They have the most market share and spend most of their breath defending Vista, stating that it isn't as bad as it's made out to be. They're mostly right. They tend to help you when you look for help, and they may have some blinders on when it comes to Microsoft's problems. But overall, they're OK.
2) Linux fanboys should really be broken out by distro. Ubuntu fanboys are easily the most supportive and helpful of the bunch. The more esoteric/difficult the distro is the more likely you'll get some RTFM comments.
3) Apple fanboys have a few problems. First is the blind allegiance to Apple, the reality distortion field that Steve has created has somehow spread into their brains. Every release from Apple becomes amazing, ground breaking and brilliant. Everything Apple does is great and must be defended viciously. Secondly, Part of the problem is that some have great technical expertise, but many know about as much about their computers as they do about their televisions. Third, and what I find the most depressing, is that their attitudes are a complete smack in the face of the tradition of hacking that founded Apple and the entire industry. Comments along the lines of "Anyone who tries to build their own Mac from spare parts is going to get a miserable experience and should be sued for breaking the law" are really depressing to anyone who knows the California spirit that started the whole revolution. If the Apple fanboys had their way, Woz and Jobs would still be in jail for selling blueboxes back in the seventies.
4) OpenBSD fanboys can be helpful, but are more like the Linux peeps you talked about in your original post.
5) FreeBSD types are helpful, but they also think people should read a book or two on FreeBSD before tackling it.
Most of them are ground breaking and amazing. You're just not permitted to speak out about either the few that aren't or if Apple's missing something. A lot of it comes the desire for some kind of over inflated self image. If Apple is fallible, so are they.