The alcohol is necessary if there are any secretions, such as oil from your fingertips. Otherwise water and a soft cloth is fine. If you really wanted to baby your screen, its good to remove the loose dust on top first with a separate cloth, so theres less chance you'll put scratches on the screen.
I did want to mention that I know people who just wipe the screens with whatever they have handy (paper towels, windex, cinch) and their screens have held up surprisingly well, so I am beginning to think the coating on the LCDs are pretty durable.