It's important to know that googlers are encouraged internally to do interviews (for extra cookie points? I don't know :P), they're assigned randomly to candidates for most of the process, so they're not a part of the whole process, just a piece of the machinery. No one oversees the interviews to make sure questions are not repeated and that there's a logical thread from one to the other (especially the onsite interviews), and you might not even be asked the questions that are actually relevant for the position they're considering you for, when you're in the latter stages of the process.
The stories I've heard from the hiring trenches are all pretty much the same. It's a great company, but their hiring processes are very weird.