On the night that NBC announced it's keeping Jay Leno and dispensing with half its weekly prime-time inventory, Jimmy Fallon officially began his run as the next host of the post-Conan "Late Night" . . . well, in cyberspace, at least. He's vlogging at NBC to prime the pump for the 12:30 slot. And if THIS were to actually be true, we might actually think about tuning in . . .