Mike Gormally's tip explains the benefits of setting an mtext width to zero. When placing new mtext in a drawing, the command prompt asks you to specify the first corner. Place your starting point, and then for the opposite corner set the width to “0”. This allows you to type as much as you want without having the word wrap return words to the next line, or having to figure how wide the text box needs to be.

NOTES FROM CADALYST TIP PATROL:  You can work with mtext widths set to any length or to zero.  If it has a length, AutoCAD automatically wraps the text around to the next line.  The width can also be quickly grip edited to change the width to fit your needs.  If the width is set to zero, then the text will not wrap until an enter has been placed inside the text.   Tested in AutoCAD 2009.