I too am considering the change, I'm still on xp having tried vista and reverted back. I'm going to try the "trial" version and if I like it buy the full version, I mite even buy it if I don't like it as it is reuced to £50 atthe moment for preorder. It's certainly not essential.
w7 is not essential, but as we are nearly all computer addicts we love to try new things! seriously though, i have been using both the beta and rc versions and i think w7 is going to be really a good OS for microsoft. i'm very impressed. i would recommend anyone who didn't go with vista but stayed with xp to try it. just make sure your present machine can handle it. a fast processor and good size memory, 3 or 4gb i'd say, minimum 2gb.