People are using Views 3.x in production. However, I recommend that only to Drupal experts who are comfortable digging deep into Views' code when they run into something, and people who are comfortable with the possibility that an upgrade might cause API related problems that could take some effort to understand and fix. The biggest weakness of Views 3 right now are other modules supporting API changes, but they've been coming around where possible.

from http://drupal.org/node/832436