(Semi-spoiler alert. I've read up through page 85 / chapter 5.) Wow, things have been moving awfully fast already! So, what did happen when Harry's wand attacked Voldemort seemingly on its own? Here's my guess: In intentionally sacrificing himself for Harry, Dumbledore has placed a magical protection on Harry, similar to Harry's mother. The magic is somehow connected / channeled through Harry's wand, which has one of Fawkes' tail feathers at its core. There's phoenix magic at work here.
So how did Snape discover the plan for moving Harry? Who was his carefully unnamed source? Did he do it though legilimency? Even though I still think he's not truly on the dark side, I don't think any of the other Order members would have trusted him completely. I don't think it was just Hagrid's loose lips after some drink, as was suggested. There's a surprise lurking there.
I thought Ted Tonks was supposed to be a muggle. Though we didn't actually see him do magic, he says that he healed Harry's wounds, apparently magically. Hmmm.