I've blogged this before, and I'll blog it again:
If you want unlimited free advertising through blogs, Facebook, Twitter, and word of mouth — JUST ASK.
Click on the image of the Zappos order confirmation page. They ask you 8 times to agree to be a friend. Result: 292,000 followers on Twitter, 12,000 Facebook fans, and countless daily referrals.
You could spend millions to build a 292,000 name email list with less sales impact. You could spend $1 or $5 per lead to get referrals from search engine marketing that are less effective that the ones you get for free from a tell a friend form.
Every business can do this sort of simple stuff, for free, today.
What are you waiting for?