Well I want to make sure that nobody assumes that just because I am not aware of any major website using ZF2, that its necessarily a fact. Quite likely nobody in the ZF2 community heard that both opensky.com and exercise.com launched on Symfony2 2 years ago.

ZF2 had it's first formal release this week, so the odds of any site running a release candidate formally are pretty low.

After any major release of a framework, there will be a shake out period.. so the long term stability of Symfony is a pretty compelling point to me.

well for Symfony2 there were two major sites running on Symfony2 pre alpha versions (2 years ago) .. and several others more in alpha. Obviously these teams had to spend a fair bit if time keeping up with all the BC breaks before the stable release, but it helped a lot in ensuring that Symfony2's stable release was ready for the real world.

We were running pre-alpha back then, too :)

The performance over our previous ZF app (practically 1-to-1) was huge!

Upgrading was a pain each time, but as a result we all become intimately familiar with the internals and even contributed a fair bit to the core.