You don't really have passionate users until someone starts accusing them of "drinking the koolaid." You might have happy users, even loyal users, but it's the truly passionate that upset others enough to motivate them to say something. Where there is passion, there is always anti-passion... or rather passion in the hate dimension.
If you create passionate users, you have to expect passionate detractors. You should welcome their appearance in blogs, forums, and user groups. It means you've arrived. Forget the tipping point--if you want to measure passion, look for the koolaid point…..
Remember folks, we aren't going for user satisfaction. We aren't going for happy. We're going for all-out passion. And that comes with a price tag. Detractors. Lots of them. And they talk. For every passionate user out evangelizing you to everyone they meet, a koolaid-hunter will do his (or her) best to make sure everyone knows that your passionate users have lost their minds. That they're victim of marketing hype. Sheep.