Michael Wines reports for the New York Times that the government of China has now barred tourists from entering Tibet. There was no official announcement, but travel agencies have been told not to organize tours to Tibet until after April 1. Although China says tourists may apply for permits to enter Tibet, there is no word as to when the permits will be processed.
All accounts I have seen say the first day of Losar passed quietly and peacefully in Lhasa, which is under heavy security. There still reports that many Tibetans are avoiding Losar festivities as a form of protest.
See also Malcolm Moore in The Telegraph (UK), "The situation in Tibet is critical, but the Chinese are not talking."