If I own it, I just doodle a star next to it...maybe even circle the page number to see it while I'm skimming. If I don't own it, I use little sticky tabs to note a page.
Well, I've never marked important parts in books, I only do that when I need to remember what page I'm on while reading, which I do by folding the top corner.
As for quotes, I memorise them, quotes that I consider good, deserve to be memorised, that, and I mostly talk in metaphors to prove a point, or explain something, and Quotes tend to help in that area. :P
Sticky notes and in the latter memorize
Ahh! No! I don't highlight books! Or dog-ear them! That'd ruin them! I make a note of the page, or, if it's short, just write down the quote. Or nothing at all. Much better than making a mess of my lovely books. :)
Yes I would never commit a crime, damaging no matter how little on my book is out of the question.
None. I don't want to ruin my precious books ;n;
i write down page number then paragraph number and then number of lines down
I use a highlighter or I underline the quote. :)