There is probably a preference in iMovie to copy to library on import OR reference original location.
Quicktime issues? Could be anything. Down res them to something smaller perhaps when exporting to QT.
This is why I quit working as an assistant editor. IT SUCKS. Seriously. Editing is the most soul sucking tedious shit you can do, and you're not even getting paid. Quit while you're ahead.
Thank god you said this, I was beginning to think it was just me.