One of the saddest things about this whole Display Names thing is we are throwing away our culture.
Fistname Lastname has been the way it's been since the beginning. As new Last Names are made available, old ones are retired. Whenever you see someone sharing your lastname you know they joined SL around the same time as you did.
I'm going to be sad to see this go, just because some people are too lazy to choose a last name. The system worked very well to let people use pretty much any firstname they want, with the neat side effect of creating these "family names" based on when you join.