This is for things that we never really found out, the questions that were never really answered.
My first major question that i never had answered was what was the nature of the relationship between Petunia and Dumbledore, do you remember in #5 dumbledore sent her a howler saying, remember my last.

this always confused me, does anyone have any other unanswered questions or an answer to this question?

I don't think there was a lot of interaction between Petunia and Dumbledore.
I think the "last" reference was to the fact that Petunia wrote a letter to him when she was a kid, begging to be let into Hogwarts. So they'd had more than one letter exchanged between them. Plus, I'm pretty sure Dumbledore wrote to Petunia every year to check up on Harry. It would not be funny if Harry contracted dragon pox or something and they didn't know how to cure him or whatever. I think, before Harry went to Hogwarts, Petunia was probably sending Dumbledore a yearly update on Harry.

that is a really interesting thought. i can definitely see Petunia being required to check in with Dumbledore. it would have been hard for her not to because of her secret fascination with the magical world. but it also would have been difficult because of her jealousy and bitterness that she wasn't magical. I always wondered what it was she almost said to Harry before the Dursleys went into hiding in Deathly Hallows. there is a lot about Aunt Petunia that is left hanging. maybe pottermore will clear some of it up =)