Yahoo has announced that they will be shortening the length of search ad descriptions from a maximum of 190 characters to 70 characters.
Starting in May 2007, Yahoo Search Marketing will require you to fill out a “short description” that would be the default ad text source. In June 2007, Yahoo will begin using shorter descriptions. If there is no short description available, Yahoo will shorten your long description to 70 characters.
This change was expected with the launch of the new Panama ad system.