Bill Slawski (of course). Just look at this post from a Cre8asite thread on how to spread your traffic levels out so as to avoid becoming reliant on Google (a great thread idea from Ruud). There's so much good stuff I want to copy the whole thread:
...I'm not suggesting that you spam reporters, but some friendly, personal emails to the right folks could get your site noticed, especially if you have something on it that will capture their attention. It's nice when you have a site that is profiled in a national newspaper like USA Today....
...By starting conversations with other people, and becoming involved in a few different communities on the web, you can become part of a number of different communities on the web. Communities that grow, shrink, evolve, and change. Forum signature files can have some of the same effect. Web rings were an approach that had a similar effect....
...By extending your reach on the web with an RSS feed, you build an alternative way for people to become aware of your site, and to visit. And there are lots of RSS directories out there (and blog directories and search engines) which spread out the reach of your site....
Ruud was right to bring this topic up - becoming reliant on Google for 70-80% of traffic has to be considered a huge liability. If you can drop that number below 50%, you're on the right track, but to be truly "safe", my opinion is that no single source (unless it's direct type-ins and bookmarks) should be greater than 20%.
Your opinions?
You know, I get so piffed when I see forum threads that start with some poor dude saying "I just lost a bunch of Google traffic, my business is in trouble" and end with a bunch of self-righteous know-it-alls telling them that they should have had a more diversified strategy.
It doesn't matter how much you try to diversify, how carefully you attack other channels, a large presence in Google's organic results delivers too much traffic to make a "diverse" strategy realistic. When the firehose of traffic starts coming, businesses react by adding staff, ordering inventory, leasing warehouse and office space, etc.
If "only" 20% of your traffic comes from organic SEO, that's pretty diversified, but if it all goes away tomorrow, you might still have 20% more inventory, 20% more warehouse space, and 20% more staffing than you can afford.
How do you deal with it? Improve opt-in and conversion rates, run PPC campaigns even if you don't fully fund them so that you can optimize your campaign and landing pages. Build relationships with visitors and customers. For most sites, it's not "if" they'll lose a big chunk of SEO-driven traffic, it's "when" and for how long.
I've seen people weep after losing a Google listing! However, look carefully at your revenue streams. Natural search traffic may be your carpet walkers and not your buyers. If your business model works, don't try to fix what ain't broken!