Every now and then, Nintendo will throw out some information in a press release. That's about it.
IIRC, WM+ install base is about twice the size of Wii Sports Resort's sales.

"The worst part about these reviews is they are [subjective]--and their scores often depend on how drunk you got the media at a Street Fighter event." — Mona Hamilton, Capcom Senior VP of Marketing
*Image indefinitely borrowed from BrainBoxLtd without his consent.







