Wired had an excellent article in January 2003 that explains what Don't Be Evil means at Google. The article, "Google vs. Evil," headlines:

The world's biggest, best-loved search engine owes its success to supreme technology and a simple rule: Don't be evil. Now the geek icon is finding that moral compromise is just the cost of doing big business.

As Google grew, the company had to answer some difficult questions:

Should Google play ball with repressive foreign governments? Refuse to link users to "hate" sites? Punish marketers who artificially inflate site rankings? Fight the Church of Scientology's attempts to silence critics? And what to do about the cache, Google's archive of previously indexed pages? In April, the German national railroad threatened legal action to remove an obsolete site containing sabotage instructions.

Most major companies refer to a detailed code of corporate conduct when considering such policy decisions. General Electric devotes 15 pages on its Web site to an integrity policy. Nortel's site has 34 pages of guidelines. Google's code of conduct can be boiled down to a mere three words: Don't be evil.

Google has struggled with these questions, and has been criticized for sometimes giving in.

But here's the kicker:

There is no wiggle room - no gray area whatsoever - when it comes to those who attempt to subvert the power of Google to their own commercial ends. One thing Brin is sure of: On the side of evil lies trickery.

I ask Brin to imagine, for a moment, running his company's evil twin, a sort of anti-Google. "We would be doing things like having advertising that wasn't marked as being paid for. Stuff that violates the trust of the users," he says, describing a site that sounds not unlike the pay-for-placement search site Overture. "Say someone came looking for breast cancer information and didn't know that some listings were paid for with money from drug companies. We'd be endangering people's health."

The article is well worth the time to read if you want to understand Google or the challenges in making the right decision when you're pressured to compromise your ethics to make a profit.

Here's the concluding paragraph:

It's inevitable that a company of Google's size and influence will have to compromise on purity. There's a chance that, in five years, Google will end up looking like a slightly cleaner version of what Yahoo! has become. There's also a chance that the site will be able to make a convincing case to investors that long-term user satisfaction trumps short-term profit. The leadership of the Internet is Sergey Brin's to lose. For now, at least, in Google we trust.