I would think join date would be a bit misleading, seeing as I believe mine states my forum join date being in January of this year, when I've been playing since open beta/CE early start.

That aside, it'd be nifty to have a little badge in the avatar area somewhere. Yes there are pitiable people who would (and will) hold their seniority over newcomers; but in truth, it's not the shiny badge, it's how you wear it.