I think the main reason bitcoins will become mainstream is because it is anonymous and you do not have to pay currency conversion fees like the other payment processors you mentioned.
![Huh](https://bitcointalk.org/Smileys/default/huh.gif)
Bitcoins aren't anonymous, they're pseudonymous.
pseu·don·y·mous/so͞oˈdänəməs/
adjective
writing or written under a false name.
Read more about it here:
http://bitcoinsimplified.org/learn-more/anonymity/4chan is anonymous, because there are no usernames and no way to tell who posted what/follow anyone.
Bitcointalk is pseudonymous. I don't exactly need ID to sign up, but people can see everything I do and link it back to one single person.