How much does it matter to you? How close does it have to be to the story inside the pages of the book? Say if the hero has a scar on his chest in the book but no scar on the chest on the cover. Does that irk you?
Or there's a tatoo that is distictive and mentioned serveral times in the book. If it's not on the arm on the cover do you feel jipped?
Me, I like to think the person on the cover is the hero or heroine so do I feel jipped. Sometimes. Am I pissed, not really. But when the cover matches the book exactly I do remember it better.
What about you?