Between QuarkXPress 6 and 7, numerous improvements were made over previous versions. Some, like the innovation of projects, OpenType support, and, of course, transparency, are huge. Others are more subtle, like multiple undo which allows you to back out of some mistakes you may not yet realize–like linking and unlinking text boxes.
Accidentally pour the article into the headline box? Did you unlink with an errant click? Just press CMD+Z/CTRL+Z and the last link/unlink operation is reversed.