Half of MSNBC's morning viewers have fled the cable channel since it fired Don Imus last month, according to Nielsen Research. The ratings company said that while in March the Imus time slot drew 316,000 households, the number dropped to 177,000 during the first month of Imus's absence. Meanwhile, message writers continue to bombard MSNC demanding that Imus be reinstated and asserting that they will refuse to watch any MSNBC program or buy any products advertised by the channel until he is.