At first, fans politely applauded the Roma performers sharing a stage with Madonna. Then the pop star condemned widespread discrimination against Roma, or Gypsies - and the cheers gave way to jeers. The sharp mood change that swept the crowd of 60,000, who had packed a park for Wednesday night's concert, underscores how prejudice against Gypsies remains deeply entrenched across Eastern Europe. Despite long-standing efforts to stamp out rampant bias, human rights advocates say Roma probably suffer more humiliation and endure more discrimination than any other people group on the continent.