Well, the whole 'eighth book' thing may have been blown out of porportion by some people because all she has really said about it (recently) was 'don't count it out' basically. It was never really a 'yes' nor really a firm 'no'. She first said it on 'Oprah' and then she was asked it again at a premire screening of HPDHP2 (at the London one, I believe) and said the same thing; 'don't count it out'. So, you could really interpret it anyway. Personally, I don't think it would really be about Harry himself. I think it would either be about the Maurauders or about the kids. Who knows? She might be planning out her next book/series right now. For some writers, the planning stage itself can take a really long time. I don't think she is quite ready to put Harry's world to rest, even if she has already put Harry, the character, to rest.

(Here's the link that I had found out about this: http://perezhilton.com/2011-07-07-jk-rowling-hints-she-might-write-another-harry-potter-book. LINKS FTW.)