GameSpot, along with other news outlets, is reporting on Wi-Fi Connection difficulties experienced the first night Mario Kart DS became generally available, leading Nintendo to post on their Wi-Fi Connection website that the Mario Kart hub was "experiencing intermittent problems".
We here at N-Sider also noticed some problems with the system; members of our staff who have been playing advance copies for the past several days noticed a decidedly less-stable system last night. Hopefully these are just growing pains, and Nintendo Wi-Fi Connection will be able to offer stable service to all comers in the very near future.