IMO, the One to One program doesn't physically scale.
Most One-to-One customers can only do their sessions "after work", which means either on weekends, or after 5PM on weekdays. So what happens is that you have a huge amount of customers trying to reserve a relatively few amount of training sessions. End result is that many One-to-One customers feel that they wasted their money on the program, as they're lucky if they can get one session a month.
As for the physically scaling part, ... the Apple Store I worked in was good about promoting more employees into Creatives as the customer demand grew, but it's to the point now that on weekends, they're doing so many simultaneous One-to-One sessions that they're forced to use computers on the sales floor (because all of the spots at the Creative Table are filled). They'll even use the handicapped-accessible table that pulls out from the Genius Bar to do sessions some days. They're out of physical space.
They could easily have the staff to do 50 simultaneous One-to-One sessions. There's just no room to do it.
Anyhow, it's crazy. I think the overall idea of the service is great, but if you can't get a session, or if your session is going to be on the sales floor (where it's so distractingly busy and noisy), it doesn't live up to Apple's promise.