The Dresden books do have killer opening lines, don't they? I think they're the best I've ever seen.
The exact impact of the opening lines depends on the reader, but you capture a bigger percentage of the readers if the opening is catchy for some reason. I don't think anyone has ever said, "The opening of the book was so great, I just had to put it down!" So, it helps more than harms to have a good opening. Which is obvious, I suppose. Anyway.
For me as a reader--I tend to keep on trucking for a while, so if the first line isn't near literally on fire ("The building was on fire, and it wasn't my fault.") I'll keep going a bit more to see how it develops within the next few pages, but some people won't.
I don't think openings can ruin an entire story, but it can kill a book. Meaning, if the actual story is good, it will shine despite the opening. IE, Harry Potter (for some people). Kushiel's Dart (first 100 pages is a slog to some.) However, if a person drops a book because of the opening, they'll never get to the story-that-is-good. So an opening can kill the success of a book.
It's like a little town in a valley. They might make some killer jam, or crafts, or folk dancing, or hot rods, or something, but if the sign on the main road is too small, or not appealing, people won't be persuaded to make the trip into the town. They'll pass this great little place by, not ever knowing it was there. And all the jammeries and hot rodders will close up shop and start new careers in accounting. Or something.