Figuring out how to refer to people can become challenging at times. At least when the majority of the people involved have LJs, I can just use the username. Even so, it gets annoying to type, and reading it feels more like name-dropping than communication. However, when people don't have LJs, I end up falling back on initials, which just doesn't work so well.
For example, there were two Ms at the party Saturday night. I can't give M the hostess her last initial, because then she'd be ME. ;-) However, calling her MtH is almost as bad, because the other M's last name begins with H. Meanwhile, there were two JCs and a CJ present. Only one of them has an LJ, to my knowledge.
And the four people who declined the invitation? Every single one of them is a duplicate initial, although at least they all have LJs. And, of course, since they weren't there, I don't need to talk about them - but imagine if I did!