Over at the Official Google blog, Dan Russell of the Search Quality team, has written a lengthy post on field studying search behavior. One of the things Russell discovered is that there is often a disparity between what people say they're searching for and what they actually do search for.
There's also a disparity between what they searched for and what they remember searching for later on.
Another area Russell dives into is eye tracking. Here's a video showing the eye tracking of 3 different people searching for "school backpack."
Last but not least, Russell explained the discovery that the "Advanced Search" page was really turning searchers off. They often were so overwhelmed or uninspired by the options, that they left the advanced options blank. They used that information to re-design the Advanced Search page.
All in all it was a nice little insight into how Google doesn't just use tech testing such as Website Optimizer or Analytics to create a better experience for their users, but watching actual human behavior in person is extremely useful as well.