I found this application the other day that will link a viewport scale to a line of text, and if the scale changes the text will automatically update when you regen. It works great! The only problem is the scale ratio is the wrong style for me.. (it displays 1:8 and i need to show 1-1/2"=1'-0")
Does anyone have an alternate version of this utility? 
 
This is where I found it..
 
http://www.cadforum.cz/cadforum_en/download.asp?fileID=274

This utility is metric only. It is a rather old software - its functionality can be now duplicated using AutoCAD FIELDS in newer AutoCAD versions. You can try [CMD]FIELD[/CMD] to get the results you need.