When will Laravel 4 be released?
Per Taylor's announcement at Laracon it will be released in May of 2013. Further on the wiki there is a time table for the next 4 releases.
Is Laravel 4 stable enough to use in production?
I would say yes. At this point in development there are a lot less items up for change. In the previous months I have seen major things change and break existing sites that I have running Laravel 4. These types of events have calmed down lately. I feel comfortable launching a site in Laravel 4 today. In fact, if you need a start in Laravel 4, check out thestarter site on github.
Release date is May 27th 2013!