Just echoing what SntCasado has said here.
You mentioned that, when first starting out, start-ups should use channels the incumbents can't/won't focus on because they're looking for scale: mailing lists, forums, and I guess blogs or podcasts would fit here as well. This resonated with me as I'm working on a concept in travel (obviously a highly competitive industry with the incumbents spending incredible amounts of $$).
This definitely stood out to me and is a point I'd love for you to give a bit more color around (e.g. examples of start-ups that did this well?).