I have reason to believe that the number of Wiis on launch day is going to be pretty good, but not mind-blowing.
I've learned that the retail chain I work for (Fred Meyers) knows exactly how many (already recieved?!) Wiis the company is getting FOR LAUNCH DAY. 5,000. That's going to be divided between 130 stores which comes to nearly 40 units for each store. We got about 20 Xbox 360s on launch day, so this is certainly an improvement, but I'm betting the big difference is going to be the run to Christmas. Between Thanksgiving and Christmas my store got about five 360s! So there is a lot of room for Nintendo to make a big difference.