I purchased all the combos I could for my website. For one, I did not want anyone else to buy them. As far as using them for SEO, totally possible but each website should be it’s completely own design, text, graphics, seo etc. Buying 4 domains and have them all be exactly the same can hurt you with google. Googles spider might look at them and think you are trying to cheat the system. What I did was a permanent redirection (301), which tells the google spider that domain content has been moved to this new domain. Your most common code you will see on the net is the (404) page can’t be found. Pretty sure those redirects do 0 for my seo and traffic though.
I’ve had numerous ads sent my way telling me they can get me ranked higher in the search engines, researched and read articles on the subject, and I still am perplexed on how it all works. 
When I type in a search using my full name, I dominate the first two pages. It brings up a listing of just about everything I have ever published on line. I think my best bet utilizing a domain, is to use it like I would a business card. The trick to a business card is to get it into the hands of as many people possible. Using your domain should be no different, publish it every where you possibly can. Write how to articles, ehow.com is a good example. Those that can do good youtube videos, do them. Publish your domain name in every forum or post you make. Post in every free business directory available. I think the articles I have read which suggest the key to marketing online is to get yourself published in as many avenues as possible, seems to be winning my personal poll.
Joie ~ N. CA
A lot of good tips in Joie.
I agree with Doug. It’s not a very important factor … but if it is possible go for it! However, it is more important to utilize keywords in your page ‘title’ and ‘link’ text, lastly have plenty of original content. If you read the official google blog you will consistently read of the importance for good relevant content. Google never explains their algorithms, but if you want a translation: write good content with your keywords relevantly displayed throughout the text … the algorithm is obviously written to ignore your meta tag keywords in favor of searching the content of your site and coming up with its own list; which will effect your search rankings.
If all things are equal between you and your competition then the domain will give you that extra bit to win.
However since things will almost never be equal, since traffic to your site can come from all different forms of advertising, including offline, I would focus on a memorable name for your business and make sure the domain is available.
The shorter the better. Something someone can read at 55 MPH in the blink of an eye would be ideal. I actually wish my name was shorter but they were all bought up.
Which brings up the next point, don’t pay more than 9 bucks for a domain.
I would have loved to get a domain like duck.com or windows.com
As far as multiple domains, the question you have to ask yourself is do you want to spend your time promoting one domain or multiples? I would much rather spend my time cleaning windows and promoting a single domain.
