Man, a bad week for top Clinton strategist, Mark Penn. First he's caught giving Columbia advice on how to push Congress for free trade in direct opposition to Clinton's stated policy. Then he apologises and, in doing so, manages to anger the Columbian government which fires his firm. But the unions still aren't happy and so now Clinton gives him the axe (in political terms he 'resigned') as well. But there's enough double-speak in there ("...will continue to provide polling and advice to the campaign") that the unions aren't likely to be mollified anyway.
Supposedly, Penn's been on the edge for a while and rumor had it that the only thing keeping Clinton from firing him was that she couldn't afford to -- she owes him something like $3mil for campaign services rendered thus far. I doubt he'll ever get paid (these sorts of things between 'friends' tend to get comped) but this gave Clinton a handy reason for dumping a failed strategist without overtly admitting that she was firing him for running her campaign into the ground.