Well now you can swap your star points for Wii points! The exchange rate is 4 stars to 1 Wii point, you can only buy card codes in denominations of 100, 300, 500 and 1000, and your Club Nintendo account must be linked to your Wii Shop Channel account.
There is a catch, rather two catches:
1. Any stars you registered before June 1st 2007 will expire on June 1st 2008. Newer stars will expire two years after registering them.
2. Nintendo's stars to Wii points exchange page has crashed or running very slowly as hoards of Europeans rush to buy Wii points. Also, all the Wii point cards are sold out!
So if you're lucky enough to get the page to load, you'll also have to be lucky to find some point cards still available. Oh, and you can only buy two point cards per day.
http://wiipointscard.nintendo.co.uk
The Club Nintendo main site has been redesigned if you didn't already notice, and there are much nicer things available to buy with your stars like a cap, t-shirt, remote-control Mario Karts, and if you can stretch 15000 points:
