When I was a younger man, I worked for a store called Waldensoftware in the Tyson's Corner mall in Northern Virginia. This was a solid job for a 16 year old kid who was into computers. The store sold computer science textbooks and software for PCs and Macs.
Often, they would loan us out to the main Waldenbooks shop in the more heavily traveled part of the mall, and we would shelf and sell books. The thing I remember from working in both locations most is 'shelving'. Shelving is the practice of tidying and facing books on the shelf so that they don't look disorganized. Flip, cover, flip, cover, align, lineup, flip and cover. You can even subtlety promote some books and deemphasize others. For instance, in modern parlance, Neal Stephenson (of Snow Crash fame) has no need for any more publicity to sell books, but since he's often placed not so far from John Scalzi (a newish up and coming science fiction author) you could face the Stephenson books spine out and the Scalzi books cover out.
Those coming in for Snow Crash can always find it, and maybe, just maybe, they'll buy a copy of old man's war in the process. They get to read about Hiro's adventures amongst the loglo and maybe discover a new author. Everyone wins!
Here's the thing. Now, some 20 years later, I still do it. If I'm in a bookstore, I can't not do it. If the shelves are even slightly uneven or in disarray, I start shelving. Flip, cover, flip, cover, align, lineup, flip and cover. It's weird. I find myself doing it unconsciously. It's startling really, it's like my body decides to go do things why I'm otherwise engaged. It's plain weird.
This happened a few days ago when I was at Border's in Palo Alto. We were looking at guide books for an upcoming trip when I look down and *poof* I'm shelving.