Alternate / Multiple domains

Recently I was asked by a client:

I thought I should ask you what it would cost us to host the 5 other URLs we registered as separate one page sites? It may not be the best use of our budget for us to do this. Is there any other way we can take advantage of the fact that we own them?

Are the domains easy to remember? Are people likely to type in the domains directly? Unless the domains are ones that people are likely to type in directly, you won’t have any significant advantage by using them. (I know there are some SEO 'experts' that tell you otherwise.)

Though I wouldn't (I'll outline why shortly) yes, you can create new sites. Remember you will need to keep the content different from your main site – otherwise you will be lowering Google rating of the new sites and your main site. Alternately, you may point these domains to your main site directly. (The right way to do this is to use what is called a 301 redirect. More info is here: http://www.google.com/support/webmasters/bin/answer.py?answer=93633 )

If building new sites, they MUST have unique content – different to your main site. The best reason for having more than one site is because there is a genuine case to have a second business that is different from the first.

There is a danger in doing this, specifically Google says:

Google's aim is to give our users the most valuable and relevant search results. Therefore, we frown on practices that are designed to manipulate search engines and deceive users by directing them to sites other than the ones they selected, and that provide content solely for the benefit of search engines. Google may take action on doorway sites and other sites making use of these deceptive practice, including removing these sites from the Google index.

The goal is usually to simply get more traffic / business - and the mistake is to think that more domains = more traffic = improved rankings on Google. However, Google is clear in that it takes into account the importance of the whole site, and is at pains to say that it's ranking system is complex and metrics are varied.

So let's say you do register a new domain, and build a new site. There are potential problems that need consideration which include:

• Google's rules
  If staff at Google think your new site was specifically designed to increase your main site's ranking, then the new site, and your main site might be removed from Google's search list. While writing this I searched for "sites de-listed by Google" (without quotes) and got 815,000,000 hits - there are plenty of sites that have been delisted for not conforming to Google's rules. For this reason alone I urge anyone thinking of registering domains and having multiple sites for the purpose of increasing their rank on Google to follow this simple advice: don't take the risk.
• Duplicate content
  Assuming that the subject is the same as the main site, developers simply copy then adapt the content from one site to the other. Google states that it downgrades sites that have duplicate content.
• Managing multiple sites
  There are direct costs of doing this.
• Opportunity cost
  Putting effort into a new site equates to not putting that effort into your main site. 
• Lost ranking
  Let's assume that the content on the new site is great and attracts traffic. That additional traffic split across both sites might see both sites at number 100 - but that same content put inside your more important main site could be top 10 material.

The maths works something like this: 

(Note there is a risk if Google deems this new site as a feeder site then BOTH sites may be delisted from Google).

• Alternate / Multiple domain names don't help get additional traffic in any meaningful way
• Better results can be gained by spending the equal amount of time promoting your main site.
• Managing alternate / multiple domain names increases the risk of being delisted from Google.