Update: just saw your second post - I've never used the "General" search page that way. Trying it, I see the bars too. Am guessing it has to do with the number of hits; if I float the cursor over the little bar I get a "448 search rank" or equivalent.
[When I use the "general" page it's to search my own journal entries for specific text; for book-searches I use the advanced book-search page. Never occurred to me to try the "general" page for books before!]
I normally use the book search too, but had tried just clicking the search icon at the top and typing in a title, and was surprised to see the result. I kind of like it as a (slightly) more direct way to get to the Global Overview page.