A few things I was impressed with and didnt see in here yet where:
Invite your current wii friends REALLY easy. Just go to the mario kart channel and invite them. All they have to do is accept and your done. I invited 2 of my friends WITHOUT even using my or their wiicode!
Another :
When your racing/battling online and you finished a race/battle you get a menu: Next or quit BUT if theres any of your friends only you get a beeping sound with another options FRIENDS you can instantly join any of your friends from there!
Now all we need is voice chat and Nintendo is on the right track!