Very interesting. Those of you who have known me for a while are aware that I supported Clinton's impeachment. If it can be proven that Bush led America into war with Iraq under false pretenses, I would support impeachment for this as well, in addition to formal removal from office (though I suspect he'd resign first). I'm fair that way: both certainly count as conduct unbecoming the President of the United States, and Bush's offense would unquestionably be far worse, given the number of people killed during the process.
One problem, however, is that I have trouble believing that Nader's motives are entirely pure, given his previous political activity. On the other hand, it's safer for him to make this initial call for action than for any of the current Democratic leaders.
As I said, interesting.
EDIT: Terrance comments on it here.