Not much of a discussion so far…

Now here are some thoughts about reading books while practising.
1. Yes, at first sight, it seems like a good idea, provided (as Rosen implies) that all the movement co-ordinates have been thoroughly investigated, and the pianist has arrived at the optimum fingering/position/movement for the piece/passage. I am sure Rosen would completely agree that to use this idea if you have not yet figured out the optimum physical movements would be to court disaster since you would be ingraining bad habits.
2. However, there are two hidden assumptions here. The first one is that after you did all your investigative work and came up with the perfect co-ordinates, long hours of repetition are needed to ingrain these movements in your subconscious. I disagree with that. Personally I think that many pianists are obsessed with practice and they spend far more time than needed. Some repetition is certainly necessary, but if you have been careful when laying the foundation (that is, try to always practise correctly form the very beginning), ingraining will be surprisingly fast and pretty much permanent. I believe that the real problem is careless practice with the consequent ingraining of wrong movements and bad habits. Overcoming those is what will take years of repetition.
3. The second hidden assumption is that repetition is boring and this boredom needs somehow to be alleviated (by reading a book or by watching TV). Again I disagree. The best way to deal with boredom is to be aware of the sensations involved in the activity you are engaged in. Hence, putting your awareness into a book rather than at the job at hand is sure to increase the boredom of practice.
4. Finally, I believe that a practice session should always have a specific and clear aim, and the practice session ends when you can achieve your stated aim in a consistent manner. A practice session where you repeat movements while reading a book, cannot possibly be aim-oriented.
So here is my conclusion: Rosen’s idea makes a lot of sense if you happen to accept his hidden assumptions (practice is boring, ingraining movements in the subconscious will take hours of repetition). However I consider both his assumptions just strong superstitions amongst pianists (very strong). Furthermore, such a practice procedure would make practising with an aim pretty impossible.
Best wishes,
Bernhard.