Only a small number of DSi owners have problems playing games
A very, very small number of DSi owners have experienced issues playing games on the system. However, this is mainly a result of attempting to play dirty cards.
“As is common after the launch of any new hardware system, we have fielded inquiries from consumers about their games. To date, an extremely small number (about 0.025 percent) of Nintendo DSi owners have inquired about playing their licensed DS games, though the most common issue has been related to dirty game cards. Nintendo recommends that players keep their game cards in the original packaging, or in protective cases to keep them free of dust and debris.” – Nintendo statement