I use latest version of ZA without any problems. Some people have reported some issues, though... I have no ZA issues whatsoever.
Edit: I use Kerio latest version on my other PC, and that firewall is unbelievable good. I'm thinking to switch my primary PC to Kerio as well... although I am little bit too lazy for uninstalling, cleaning the registry, installing of Kerio... whoa... too much work, haha...