I havent seen any theory about the strange things surrounding Walt... Maybe I missed the thread, sorry in that case :P

But when Walt was still in Australia with Brian and was reading in his book about birds, the moment after, a bird flew against the window and was dead.

When Michael went to get Walt, Brian also said: "There's something about him, whenever he's around strange things happen..."

And last, but not least: when Walt was reading in his Spanish comic book, we could clearly see a polar bear in the comic book. A few moments later, Walt is being attacked by a polar bear...