1. Career progression abruptly halted once I reached the Genius role. I started off with Apple as a part-time sales advisor ('Specialist') and successive promotions happened quickly, but the Genius position sits in a comfortable little cul-de-sac thereafter. Geniuses in Apple Retail are remunerated well but cannot easily continue a technical career into Apple Corporate as there is often a qualifications barrier to entry. Perhaps understandably, Apple does not have a career pathway that allows Geniuses to train for Corporate roles in the absence of degrees in computer science, electronic engineering or similar.
The general consensus seemed to be that while there is no stigma attached to working for Apple Retail, it is held at arm's length from Corporate and aspirational talk from management about moving across as part of one's career path is largely lip-service. Multiple colleagues of mine had secondments to Corporate but were not offered permanent positions. My advice is that if you want a role within Apple as a wider organisation, it is better to gain more relevant experience elsewhere than get your foot in the door with Apple Retail.
2. See 'Advice to Management'.