On the events viewer which is where the video is originally stored,
the option of rejecting clips is there. Often (actually about half
the time), when I mark a clip for rejection and then click the delete
button (or use the menu for the same thing), iMovie will freeze. The
only way out of it is Force Quit. Normally, this might not be a
problem except that when this happens, the entire event is gone, not
just the marked clip, when iMovie reopens. When it works right, it is
great and saves hard drive space; when it fails, it still saves space
but at the cost of losing all the video.
I have had real reservations about the newer version of iMovie
"helping" me by always saving without me saving it. This is one of
the places where it truly matters as it isn't allowing the previously
saved version to be available when this happens.
Learning point: Never overwrite your video tape until your DVD is
completed because the newer iMovie cannot be trusted if something goes
wrong. Fortunately, I have not lost anything because of this but it
is annoying to have to copy it back to the computer. The reason I
love my Mac is that it doesn't do things like this! It's a bit ironic
that I switched to Mac because of iMovie and it is iMovie that is
causing the frustration . . . such is the way of the world of
computers.