How much does cover art influence which books you buy?
Personally, being a very visual person, I greatly enjoy cover art that I find pleasing to the eye. Great cover art always attracts me to a book, but of course I'm not going to buy a book I really don't want to read just because it has a gorgeous cover that I find extremely attractive. Nor am I going to pass up a book I've been waiting to read just because the cover art is less than appealing. (This is the case with the book Animal's People by Indra Sinha. The British cover art was passable, but the US cover art is, in my eyes, an abomination and does this book, which many British readers just loved, a terrible disservice. However, I've been waiting and waiting to read the book since it made the Booker longlist, so I'll have a copy in my Barnes and Noble shopping bag the day it's released in the US.)
Now, if I'm torn between two books and only want to buy one, I might go with the book with the best cover art. And, if I'm browsing, and I love to browse, and see an interesting book, even though it's a book I hadn't planned on buying and definitely don't need, if the cover art is gorgeous, I just might find the book irresistible.
I know some people who find cover art irrelevant. While it's rarely the deciding factor for me, or for most people, I do think publishers should put more thought into their books' cover art and ensure that fact that it's both attractive and eye-catching, relates to the book's content, and is, in some way, unique.
And by the way, my very favorite cover, so far, has been the US edition of Alessandro Barrico's gorgeous novella, Silk.