John L. Loudermilk wrote to say, "Since multiline attributes behave much like mtext, I've replaced standard block attributes with multiline attributes for two distinct advantages: I can adjust the width of a multiline attribute (to fit as required), and I can mask a multiline attribute (to hide objects under attribute)."

NOTES FROM CADALYST TIP PATROL:
This feature is new in AutoCAD 2008. For more information, check out this blog entry from JTB World.