Have you ever felt like you could really relate to a charactor in a book?

Oh yes. Several times. The character I could most strongly relate to is Luna Lovegood from the Harry Potter books, but there have certainly been others as well. But I can definitely relate to Luna the strongest. :D

Of course, i find it easier to read a book where I have some similar personality traits with the character. That or its really well developed...

In every book I read. Zoey Redbird (from The House Of Night novels) and her nightmare family, Nore Grey (Hush, Hush), Lucinda Price (Fallen and Torment), Elena Gilbert (The Vampire Diaries), and so on and so on. I pag-ibig to read, so there's a lot madami than that. That's really all I have time for.

Jane Austen does that for me. Especially the main character in Northanger Abbey - her imagination gets carried away with her because she's such a book worm.
Also pag-ibig Jane Austen because she seems to understand how absurd people are - something I've only just realised and now I'm free to enjoy the change in perspective.

yes, often....you can see that the may-akda is talented when you are able to identify with the characters.
My favourite ones are the authors that manage to transport sympathy for the villians too. When you realize that you can really identify with an orc you know the author's worth remembering his name.

HP-character I identified mostly with is Narcissa Malfoy

Some, but for most, I usually change my state of mind/thoughts/personalities to be like the character I'm presently reading, so I can see how/why they think, act, speak, or why they make the choices that they do. It makes me seem like I'm the main character, and that I'm living out the whole book, not just pagbaba it.

Not really...maybe a few traits.