That depends on your deployment model. Google is live at head, with no support for past releases. In the web world this is reasonable: they control the servers and thus can force releases. I don't work in that world though, there are times where I have to support customers on older releases who refuse to upgrade (when the customer is spending millions of dollars per year you can't ignore their rules no matter who stupid you think they are). Thus I need to think about those factors anyway.