Wii Fit is a "game" in the same way Brain Age and Brain Age 2 are "games".
That is to say that the software isn't for you, the "hardcore", the type that's going to refer to good games as "AAA" titles or play Guitar Hero and Rock Band for high scores that they can post on YouTube.
The software is another branch on the Nintendo "let's get everybody to play games" tree. As such, it's critic-proof and EB Games nerd-proof and CAG-proof. No matter what you all are going to say (just like the thousands of "hardcore" game nerds that post on message boards about saying that Wii is a waste), Wii Fit is going to sell millions and will probably be in the Top-10 of software sales for this year, alongside GTA IV, Metal Gear, Smash Bros, Madden, Kart, and Wii Play, just to name half of the chart.
Oh, and as for availability, I was able to go to a Gamestop (albeit a "wrong side of the tracks" Gamestop, where the neighborhood is primarily occupied by ultra poor dayworkers and police are arresting someone in the strip mall where it is located for drugs and shoplifting (and I highly doubt people actually go to this Gamestop)) on Saturday afternoon, and bought it with no problems. This is on Long Island, and this very same Gamestop probably still has some available today.