Seth points out in his blog post, Why word of mouth doesn't happen, that for word of mouth to occur, a product or service needs to be “worth making a remark about.” I agree, but not completely. I'd add that a brand and the marketing support for a brand can be worth making a remark about. I think Seth would agree because he goes on to say that “people talk about you (or not talk about you) because of how it makes them feel...” Isn't brand the essence of how people feel about a company?
Consider Dove. It's soap (unremarkable product), but the Real Beauty campaign got people to feel differently and talk, a lot. Or Geico – it's insurance (unremarkable service), but the Cavemen and Gecko are fun to talk about.
Granted, if a product or service is dull, a marketer has a bigger WOM challenge to overcome, but it can be done without a major experience overhaul.
