I was recently browsing Slate.com when I saw a link to a slide show referencing Banksy and gave it a look. The page presents you with a link that pops up a slide show (figure 1). The navigation is simple for the slide show with standard text-based navigation at the bottom of the text. I was enjoying the pictures, scrolling through (figure 2), and then got to the 4th picture (figure 3).
Then it happened. You know, you're moving right along and then the navigation is gone. I guess there is an over-estimated amount of text for this slide, which has pushed the nav out of sight and usability. There's no scroll bar, my scroll wheel doesn't work, and I can't select text and drag down. Hmmn. I guess I'm done with this now.
This unfortunately is more common than is aware of, particularly with popped windows that want to create the feeling of a sideshow and restrict scroll bars frequently. With active awareness of the data created from Google Analytics, I have a feeling this problem could have already been corrected. I don't mean to pick on Slate - they have great content and I appreciate what they do, but this is a classic example.
Web usability isn't just about eye tracking and tendencies, it's about people being actually able to use, in the most basic form, your website.
With some investments in time in Google Analytics, this type of issue could have possibly been spotted. For example, I'm sure the data would tell us that a greater percentage of sessions ended on the fourth slide, alerting us of a potential usability issue or problem.
Through Google Analytics, this type of situation could have been spotted for automatically and drawn the attention of the appropriate person. It's also worth mentioning that you can navigate through the sideshow by clicking on each image, but if I begin my navigation through a particular convention and then it's no longer accessible I get confused and generally leave. I would submit that most others would as well - but I'd be curious to compare the data with my opinion.