Are the threat calls supposed to be taken seriously specially when they are given in virtual world? Kathy Sierra got death threat and she canceled her presentation. I wouldn’t support her if she cancels the presentation just because she is terrified from call and that’s what she seems to be.
But I would definitely support the cause to criticize such attempts by going offline as Robert Scoble does who has taken week off in order to condemn such act. Mike Arrington rightly mentions that it is better to ignore them.