not having all your eggs in one basket is very sound strategy
That, of itself, is debatable:
Behold, the fool saith, "Put not all thine eggs in the one basket"--which is but a manner of saying, "Scatter your money and your attention;" but the wise man saith, "Put all your eggs in the one basket and--WATCH THAT BASKET." (Mark Twain, "Pudd'nhead Wilson's Calendar")
However, Play_Bach's point is also an important one: "unchallenged dominance" is the problem, and it probably will take legislation rather than action by small groups to deal with it. It doesn't matter what I do to market my business if my potential customers all use Google and only Google. Even if they see my business advertised on prime time TV, they will still use Google to find it when they get to their computer. Other marketing media are more costly and less effective than Google organics, and the next best thing to Google organics is probably Adwords.
Like ohno, I have a lot of repeat customers (and good word-of-mouth recommendation) but this will always be a diminishing source. For my business to be viable I need new customers who haven't heard of me yet, and who don't know anyone who has. As I - and others - have mentioned before, "google" is widely used as a verb that means "how you find something". I still have enquiry forms filed from a few years ago, and nearly every one has Google in the "how did you find us" box. Fifteen years ago, it was Yellow Pages, and at some time in the future it will no longer be Google, but for now the alternatives are not making enough impact to fill my order book.