Contrary to what some developers will tell you, Craigslist is not evidence that design isn't important. Craigslist is evidence that it depends.
Good designs communicates what the thing is and is not. That's the kind of honesty that creates trust. Craigslist's design is not visually pleasant. It's cluttered and inelegant, all of which are good. Why? Because Craigslist is essentially a big bulletin board, a DIY marketplace. It looks like a DIY marketplace. Slick design would communicate something corporate, something with a marketing department attached, and that's not what it is. Craigslist's design is what it is.
Think of it this way: Quick, which of these two menus belongs to a joint where you can get simple Mexican street tacos for $1.50 a pop, where you pay at the counter and your food comes in a plastic basket?
On the flip side, which of these places would you choose for a date? Either way, you don't even have to read these menus to know what kind of place you're getting. You can just eyeball them. Both are successful designs, which is not the same as esthetically pleasing or even good. Any designer could improve the first one, but that's beside the point. The point is what's being communicated.
