In the business world, both real and virtual, it’s all about location, location, location. Rule number one for the vast majority of commerce is the ability to make yourself known. After all, if customers can’t find you, how will they ever buy anything from you? Or come to think of it, even know about you in the first place.
Establishing a ‘presence’ in the real world’s pretty straight forward. You literally set up shop. Find a place, sign a lease, and move into your new location. No matter what you do, if you paid to open your store in a nice shopping district, it will still be there the next day.
However, in the virtual world, where your store is your website, the rules are different. Your site’s web address may forever and always be the same, but the way people find it in the first place (search engines like Google) can change overnight. This is because Google has a secret set of rules to determine which sites show up where on their search results. These rules, the algorithms, aka PageRank, typically don’t change too often, allowing SEO specialists to optimize websites to perform well under the current algorithms.
Once in a while though, Google will update their master algorithms somewhat drastically. Usually in response to the endless amount of sites trying to take advantage of current algorithm loopholes. These sites, known as content or link farms, serve no real purpose other than to rank high, and generate traffic for ad-clogged pages. Here’s a good article in the LA Times about all that. Interesting stuff.

Google will tweak its algorithms to weed out these cheater sites, but of course in the process (because nothing’s perfect) some legit businesses are affected too. One day business is humming along online, with plenty of solid traffic to your online store — and the next, you have no customers at all. Nada. Zip.
It’s probably a good idea to keep in mind that although good Google rankings can be a serious boon to your business, it is not something you truly control. Even if you’ve got it all figured out, Google can (and will) change up their algorithms sooner or later.
Speaking of which, they did so recently. Here’s another article in the LA Times about a recent algorithm update, and how it has affected several web businesses.