I usually read novels in order, but I've been guilty of skipping to the end and then going back to read the rest (a la Harry in When Harry Met Sally, haha).
When it comes to non-fiction, then I am all over the place in a book.
In articles and things like that, I tend to do a pre-scan, glean what I want, and if it's really interesting I might read it all through. Magazines are never read front to back...I especially read interviews out of order. I will start in the middle, go the end, return to the start. I think this is because the meat is usually in the middle of almost any writing.
I totally write out of order. Thank goodness for computers....I tend to jump to different paragraphs of my post as thoughts come to me, and I copy and paste to put my posts in order. Not just whole sentences, but even the structure of the sentence may get rearranged. Unfortunately, that can cause errors like leaving a connecting word out....