Not necessary yet for me - I'll get it a week before the first Mario game for the console comes out.
I waited in line before the store opened to get one launch day.
Im not getting one for a whiiiiiiile :(
I got up at 3:30 Sunday morning and was outside my local Best Buy by 4:00 AM. Was it worth it? YES!

I picked up The Legend of Zelda: Twilight Princess, and Trauma Center: Second Opinion.
I believe it's the Wii friend code that will be used for online games, but right now what you can do with it is add people to your message board address book and send messages and Miis.

To find your's you go to the Wii Message Board, Create Message, Address Book, and your code is on the cover. From there you go to Register, Wii to add other people's.
Not getting it till something good comes out for it. Like Brawl or Galaxy.
I don't hate Zelda, it's just , well, I never really played anything of it to really enjoy it.

Plus I have better games to spend 50 bucks on.
I hear you. My birthday was the Wii Launch day, but even with all the money I received I couldn't get it. I had to work another week to get enough.

That said, the Wii is the cheapest next-gen console. If you can't afford it, well...