I don't know, while something like Kirito and Leefa being brother/sister seems extremely obvious to a viewer, I don't think it's that unreasonable. Maybe the manga goes into more detail, but the two don't seem to speak much in real life and we have no clue about how open Kirito was about his experiences in SAO.
Now, I would be willing to believe that the plot is a little ridiculous, but the poster argument is really bull. I don't know how it is in Japan, but as an American, I almost never entered my brother's room as a kid (and I'm a guy). Why would I? It was his personal space. If I had a sister, I'd be even more reluctant (not that real life logic means anything in an anime). Simply because she has the poster does not mean he's ever seen it.
I'm more hung up on how his name was still available! Kirito would be famous in the gamer community for clearing SAO, yet no one took the name and no one recognizes the name in ALO?
Spoiled for people who are waiting to watch the show.
Edited, Dec 3rd 2012 1:07am by xypin