1. It's not the home page that was linked to.

You're right. My bad. Although that actually makes it worse :-)

The words "privacy" and "private" are not mentioned on your home page at all. If that's the boards USP then shouldn't it be a little bit more prominent there?

2. It's constantly repeated how much privacy matters all over the site. I frankly don't understand what you are talking about...

Normal people will not browse all over the site. The vast majority of people will just look at the home page. You need to convince and convert people there.

Take a look at the "why us" page you linked to. I've highlighted the areas you talk about privacy

http://cl.ly/1P1c083v0r470y1m0k34

If that's your primary USP it's buried among the other stuff. And, as noted previously, not mentioned on your home page at all.

3. The benefits should be obvious from reading the manifesto.

First, people are not going to go read the manifesto. At the very least they need to understand that reading a manifesto is necessary to understand your product.

Second, the benefits of your system are not obvious from the manifesto. To be honest It doesn't read like a manifesto. It's a rant ;-) Nothing wrong with that. Rants are fun. But it's not putting forward a position of "what things should be", and it doesn't seem to talk about how the product solves the problem at all.

You're familiar with the product - you understand how it fixes the problems. The casual reader will not.

4. The privacy is not the only feature, obviously.

Obviously. But it seems to be the only one that you have that is a competition point with other forum operators. It's the reason folk will use your system rather than phpBB or Vanilla.

5. I don't understand whether you are saying that there is not even a "minimum level of visual design" or if it's "too complex", but a lot of work was put into it to be beautiful.

As a new user this is what I'm seeing on OS X Chrome

http://cl.ly/1R0d2P1e0W2B0a452T1P

which doesn't meet my idea of beautiful I'm afraid. Everything is presented at pretty much the same level of visual hierarchy. Uncommon functions like "Report" are put right next to common functions like "Reply". I could go on...

6. I haven't heard of that model, but it seems very abstract.

It's a useful one to think about product features in if you're trying to disrupt an existing market.

Have a google around - there's a fair bit written on the topic. This might be a useful start http://www.uie.com/articles/kano_model/ - especially the section on "The Migration From Excitement Generator to Basic Expectations".

7. It's no wonder that nobody uses the service since nobody knows about it and it's impossible to get heard.

All sites start with no users :-)

Getting heard is a problem. The best advice that I can give is to find a group of users who feel the pain points that you're trying to relieve a great deal - and pitch at them directly.

Two final random thoughts

1) I think one audience who might be attracted to your service, folk who are very sensitive to their personal privacy in all areas, will be concerned by the lack of information on how their data is treated by yourselves - the hosting organisation. You talk about the end-user. You talk about the businesses who might use it. You talk about the moderators. You don't talk about the hosting company, back-end security/standards, etc. There isn't a privacy statement for example.

2) The site functionality seems to mush privacy, anonymity, accountability of posting, etc. all together. There may be value in teasing them apart a bit.

For example: I've had dealings with a web forum for people suffering from chronic pain. These folk are very focussed on privacy (they're discussion very personal stuff they don't want the general public to see) and anonymity (they occasionally discuss the repurposing of recreational drugs that are illegal in some locations so they don't want their real identities becoming public) - but they're also keenly focussed on accountability (they need to know that "alice" is the same "alice" across conversations/threads because it affects the level of trust in the information provided.)