Does a great (truly) singer make for an acceptable conductor?

A review of the Met's Madama Butterfly just in from the New York Times.  Arguably the greatest tenor of our time, Placido Domingo, is now extending his career by stepping off the stage and into the orchestra pit.  This is not the first less than glowing review I have read of a musician whom I admire greatly.  Of course, even though he is nearly 71 and still (mostly) in possession of that incredible sound, Domingo is obviously too old to be convincing in the many roles (136 as of July 2011!) that he has played.

Interestingly enough, Domingo made one of his major debuts (New York City Opera) in Madama Butterfly in 1965.  He has opened the season of the Metropolitan Opera a record 21 times.  To say that he has sung everywhere would not be hyperbole. 

I have always considered him to be a class act.  I'd much rather see him bow out as a conductor than possibly become a caricature of one.