I used to back before they changed the system. Stars earned from buying games didn't used to run out, so back then I could actually gain enough of them to buy something. I also used to buy nintendo games far more. Infact I got a Nintendo VIP DS from the system, which meant you got the console 1 month early. Also got a copy of Metroid Prime from it too. Shame those days are long gone. Stars now run out after a year, and I don't buy enough nintendo games in a year to get enough points to buy anything. Infact I don't think I've even bought any games published by nintendo this year, other than Pokemon Soul Silver.
I remember being majorily pissed off when they changed the system. I had around 4000 stars saved up ready to get something, but they all ran out without warning.