I just took the train trip from Qinghai to Lhasa. Due to the influx of tourists from this new train service, the visiting hours to Potala Palace is now only one hour, although they increased the daily inflow from 1,000 to 3,000 people so everyone can get a chance to see inside. The result is a rush through the palace, with barely sufficient time to take in the art and monuments. The tickets are officially 100 RMB (US$14), but scalpers ask for up to US$100. So plan carefully with your travel agent.
One politically incorrect comment: While we see the current 14th Dalai Lama as a wise, benevolent, sagacious leader, the theocracy that ruled Tibet over the last 400 years were no angels. A system of absolute power over every phase of people's lives in a almost hermitically sealed region, with no checks and balances always lead to abuse of power. Look at what happened in the Catholic Church over history...men are men.