One of your new, enthusiastic SEO clients, especially one who owns a local business, searches Google for one of his keywords only to see one of his pages ranking very well. Only a week into his campaign, he frantically calls his project manager to relay the awesome news only to learn the truth: his search results are just that, his.

After several whadayamean's and long pauses, a history lesson begins on how Google personalizes results. He did his search from his home computer, which is just a mile from his business. He was also logged in to his Gmail account, has a Google+ profile and visits his website several times a day, usually from Google.To make it easy to understand, let's visit each layer of search personalization.

How Location Affects Search Results

Where you are in the world helps to determine which search results Google will display. More accurately, Google will use the IP address of your computer to assume your location. But why does Google care where you are? Well, that depends on the intent of your query.

According to an internal Google document meant to train human quality raters, Google is looking to figure out if you want to do something (such as visit a restaurant), know something (think Wikipedia) or go to a specific brand's website (such as Sony).

OK, so what does this have to do with your location? Well, if you're looking to check out that new Italian restaurant near your apartment (a new one opens in my town every 5 minutes), then you probably don't want to see restaurant results from all over the country.

This level of search personalization is active for all users, whether they are signed in to Google or not. Additionally, searching for something that returns a variety of places will actually change the layout of the Google result page.

How Web History Influences Search Results

In 2007 Google really started to personalize search results with Web History, which could track your movement from page to page via the Google Toolbar with the PageRank meter turned on. In 2009, Google increased personalization further by giving precedence to certain pages based on your behavior as well as listings created from your online social network.

Google's search algorithm originally gave pages a rank based on how many links it received, where the links came from and the relevance of the linking pages. Now, Google adds a human element to the calculation. If you follow X person online, you must consider this person an authority on some level. If X person visits Y page, and a connection can be made between you and person X for a related query, Google may assume that this page will provide value to you as well.

For example, if Jack visited the website for Pizza Place A and you are friends with Jack online, Google may want to show you that same page even if that page would not normally rank based on the original Backrub algorithm.

How Google Plus Personalizes Search Results

On January 10, 2012, Google did what most Internet marketing professionals expected them to do: fully integrate personalization and search with Google Plus. Read Danny Sullivan's Search Engine Land post regarding Search Plus Your World to see what's in this latest update. (Hint: you're going to see more stuff from Google Plus in your search results.)

So what does this all mean?

As a business owner with a website and an online marketing campaign it can be frustrating to know that what you see when you search isn't what the rest of the world sees. The good news is that some level of personalization has existed for years. So if your SEO campaign has continued to be successful, your SEOs have already helped your website adapt to personalized searches by utilizing the power of social media.

The bad news is that Google has changed the game yet again to promote one of their services. And now it seems that adding a Google Plus page for your business to your social media portfolio is almost mandatory if you want to stay ahead of the competition. At least until Facebook opens its data to Google.

For now, Search Plus Your World should probably be called Search Plus Your Google Plus Minus Your Facebook.

Social media popularity is already believed to affect Google's search results (for Bing, this is fact), but Search Plus Your World takes social signals to a whole new level.