I has a theory!!!
Possible spoilers follow. (We won't know for aweek and 3 days)
But I'll know before the USA people do.
The gleam of triumph in Dumbys eyes... I wonder...
Harry and Tom are linked in many ways. Through the scar, their wands, and now they share the same blood. Harry shares Toms feelings and thoughts at times. Hmmm... Why is this significant...
Know thy enemy... Hmmm...
Back to Lily, has anyone noticed a resemblance between her and the Weasleys?
"All the magical families are related somehow."
Lily might well have been an orphan somehow, in some way related to the Weasleys (because they all are). Petunias bitterness towards her "sister" and Harry might stem not from jealousy at L having magic powers, or from disliking anything abnormal, but the fact that L is adopted, and when the magic powers were discovered, Lily (the adopted child) got lots of attention...
There is no mention of Petunia in the Mirror of Erised chapter, and you'd think there would be if she was an actual relative...
So Harry and Ginny are somehow related... But distantly, and all the magic people marry each other anyway, so that's fine.