Apple’s multi-facted .Mac service is a conundrum, a riddle in and of itself. What is .Mac, exactly? What can it do for me? Is it worth it? The problem is that .Mac is more than one thing — it’s e-mail, photo and video sharing, Web site hosting, backup, and a synchronization tool all in one. .Mac is a suite of Internet Web services where the sum of its parts creates a value far greater than any individual piece.