If you go to the Wii Shop Channel, and read the "Connection Ambassador" information, you can read details about getting 500 free points just by entering a friend's Wii Code (and them entering yours).
The 500 free points can only be obtained
once per Wii. You can still help as many people as you like (to let them have the 500 free points too). There are extra bonuses for helping 10 and 20 Wii users as well (namely, getting certain VC libraries for free).
See Wii Shop for more details
Note: The person being helped has to have done this within the first 30 days of going online on WFC. So yeah, its only useful for people who know mates who are about to get a Wii.