Businessweek has an interesting story about the marketing strategies of In n Out burger. Basically, they state that word of mouth marketing and strategic placement of the physical stores are responsible for the success of the chain. Yep, I agree. But maybe the reason for the chain's success is not purely due to their wom and placements, but also because they make your burgers fresh, and they don't freeze their beef or fries. And they have animal sauce, which is possibly the most heavenly combination of unhealthy stuff you can ever have. Burger King or McDonald's' products simply aren't that good, which is why they can't have a good w-o-m campaign even if they wanted to. Because the bottom line is, w-o-m marketing relies on the quality and appeal of your product, and BK and McDonald's product just can't compete.
On another note, In N Out also has an amazing ability to keep everything related to their brand in alignment. There is no confusion about what an In n Out burger is: it's simply GOOD. And the same (simple & good) goes for everything else about the brand, their menu, their look (the arrow's been around since they started), the consistency of the colors, the burgers, and their ads. I remember hearing a radio spot for the burger chain when I was in Southern Cal, it went something like this:
Girl: I love you.
Boy: You're my double-double.
Girl: Really? Ooooooh John!
Jingle: In n Out, that's what a burger's all about...
Simple and good advertising.