I love single rider lines. But since there's no ride ops at the line, it seems to be pointless. Many times, if I do see a single seat, in the row I'm waiting for, I'll just say "single rider" and never had a problem with jumping in front to go. Sometimes you get some decent people that'll yell back "single rider" anytime there's an open seat.
I also like it at Disney when it comes to some rides like Soarin, where if they have enough for only one, two, or three, they'll go down the line looking for a group of that size.
Now what they need to do is get rid of that stupid quick queue, I hate waiting in a line that has maybe two or three groups ahead of me, and then end of waiting like 5 groups because they load from the other side.