I would have to say that a book's cover will absolutely lure me into picking up the book and at least looking at it. But at the same time, it rarely is the reason I buy a book. The other main reason I pick up a book is because I know and like the author, and that is much more likely to convince me to buy the book. I suppose it's cheating to say that the last book I bought was A Portrait of the Artist as a Young Man since I did so for this class.
As far as books bought not for class, it's been a while since I've bought a physical book because people keep giving me books to read and I have a pile I look forward to eventually reading. Instead, I tend to buy audiobooks to listen to while at work or when driving. When I'm on Audible looking for the next book to read, I rely a lot on the cover image. I'm much more drawn to covers with bright colors and interesting typefaces, like the below images. I also really like covers that aren't too busy and don't remind me of anything.