>I think I would prefer the option to somehow mark a thread so it doesn't clutter up the top right pane. However, even more expensive than your idea (unless it could be leveraged off the existing mark thread capability).

Not being a web expert I have no idea what would be involved, but one thing I think would be helpfull is to get the threads collapsed at first and expand the ones I want. That way if there is a is fox dead thread I wouldn't even know how many messages there were.