Our guild did this as a two year challenge. We had more than 2000 UFO among those that participated. More than half were completed that year. There were many smiling faces at the monthly show and tell. In addition, for each UFO completed you put your name on a slip of paper and into a drawing. The organizer went to quilt shops and asked for items from the guild... these were the prizes. At the end of the year, all the slips were put in a big jar and there were 3 major prizes... can't remember what they were ( think one was a sewing machine, another a large gift certificate from a quilt shop and the third draws a blank.
Anyway, it was well received. The gal who did it was well organized and each participant had a notebook with a page for each UFO. One lady had over 500 UFO's. She taught classes and had many samples in various stages.
We even had a section of our quilt show for showing the UFO's.