When you have a question or a problem related to Symfony, where do you ask for support? Today, there are many options: the forum, the mailing-list, IRC, Stack Overflow and probably other ones I'm not even aware of. That's too many, and it dilutes the community and our ability to help people efficiently. When someone needs help, we want as many people as possible available to answer it.
IRC is a great way to have a potentially fast answer to a question or a conversation, so we should keep it.
But the mailing-list, the forum, and Stack Overflow are working mostly in the same way. However, the mailing-list and forum are no longer the best solutions. Both get less attention than Stack Overflow, which means that more questions are left without an answer. Moderating the mailing-list and the forum also take a lot of time as we have a lot of spam on the forum, and all posts need to be approved for the mailing-list (which delays the posting quite a bit). Stack Overflow on the other hand is much more efficient, has more people looking at questions and gives us nice additional features that make it easier to find solutions.
For all of these reasons, as of today, the core team has decided to make Stack Overflow the preferred and recommended way to ask Symfony support questions.
The mailing-list and the forum are going to be closed in the next couple of days. We will keep the mailing-list and the forum in a read-only mode to keep the archives around.
I'd like to thank all the people who helped moderate both the mailing-list and the forum along the years. Nobody noticed, but they did a wonderful job at limiting spam.
By the way, if someone can invert the symfony/symfony2 tag relationship on Stack Overflow, that would be super helpful (symfony should be the main tag and symfony2 just an alias).