Like most situations, it depends! The specification is finalized so yes it's ready for prime time. The API makes the development easier (and to me more fun) so yes it's ready for prime time.
Having said that note that 1. Not all application server vendirs implement the specs yet. So, if you are set on a server (e.g. WebSphere) check with your vendor first. As of today, WebSphere Application Server doesn't implement these specs yet 2. EJB 3.0 uses some new concepts that were not available before (e.g. annotations), if you are working under tight deadlines, learning curve could be an issue
In a nut shell, only you can decide whether EJB 3.0 is ready for prime time
Mark, What makes you think JBoss is fully compliant? Not challenging you... just curious
Well, one of JBoss's employees was on the spec team, JBoss was always following the spec as it progressed and quickly updated it while the spec changed, and are right there with the final spec. If it isn't 100% compliant at this time it is at least over 90%. There isn't a certified compliance yet, but that isn't because JBoss hasn't adhered to the spec yet, it is a matter of Sun getting up to speed.
I will also say that I work for JBoss, so that you know where I am coming from.