Not for novels, or at least I try not to. I'll be honest and admit that having real people on the cover of a book makes my interest plummet, especially if it's one of those cash-grab editions of a comic. I depend more on titles and synopses.
For comics, it's kind of 50/50 ? I read mostly manga and webcomics, and still depend on titles.
If the title is a sentence (eg, "Is it wrong to pick up girls in a dungeon," or "so i'm a spider - so what?!") I know what group of genres to expect and usually steer clear. The Dead Dead Demon's Dededede Destruction caught my eye, even though the art style isn't exactly to my taste.
I find I'm way more forgiving of aesthetic than I am of storyline, lol.