Have you updated yet to Mountain Lion? If not, Apple is about to provide yet another reason to compel people to update from OS X Lion, by ending the free beta of Messages next month.
There are plenty of security-related upgrades that were introduced in Mountain Lion, which make it a much safer operating system. But some people are reluctant to plunk down $20 for OS upgrades when their existing version is still functional. (Certainly understandable in this economy!) If you’ve come to enjoy the Messages app, it may be a bit more compelling to upgrade your OS, as Apple will soon be disabling the app’s ability to use the iMessage protocol.
In order to continue using this functionality uninterrupted, users will need to upgrade to Mountain Lion before December 14, 2012.