I see a lot of advertinsing all over the net saying "You will get xxxxxx visitors ....." and stuff like this.

Somebody tried one? It is realy working? Or is just some wasting of time?
Because my feeling is that these things are not working as said. If it woold than every site whould have a very good number of visitors and everybody will be happy. This can't be. In a business somebody always looses(my opinion).

Are you talking about services that offer to bring traffic to your website
I have tried those and I did receive traffic. However, the traffic did not convert into new members. I don't even know where those visitors came from and who they were.
I don't know what technique they use to send you traffic but this traffic is not targeted (even though they promise that they will send you targeted visitors) and therefore it is not useful.

My advice: don't waste your money with these kind of services. You are better off using that money to adversite on relevant websites or spend it on adwords.