If it weren't for the fact that some of my alts are on alliance side and sooner or (most likely) later I will level them all to max to see all classes again, I wouldn't play both sides in SL. There is really not much of a point to it since there is barely any faction story and the bit that is there is stuff like Tyrande being slightly less of a cunt if you play alliance. That's not enough for me to care.