For me a good book cover is a bonus when buying an author you know - you will buy the book if it has or hasn't got a good cover.
But how about those authors I don't know? I would have thought, no it doesn't make a difference. If I recognise the name (i.e.. have heard of the author but not read anything), it might not, but maybe it matters more to me than I thought. I'm a visual person so I love looking at artwork and of course an appealing book cover would make me more likely than not to pick up a book.
I have always tried to abide by 'don't judge a book by its cover' but who knows. Next time I'm at the library or the book store I might have to check what I do and do not look at, and how much the covers actually influence me. Though I don't think it has any influence on me in category. But single title?
Some fab covers from writing friends:
Do covers influence you?