Nearly all of the first 800 people to join TalkPhysics used their full real names. The next 1000, however, have pretty much fallen 50:50. That’s about 500 people using TalkPhysics who are using pseudonyms or abreviations. So, either the first 800 names were added from a list, centrally (?), or this behaviour has evolved.
As I’ve said, I feel strongly that this should not occur on a professional networking site — and if it is something that has emerged I feel that it should be addressed earlier rather than later, before it becomes (even more) endemic.