Here's a five minute tip which can boost your organic rankings significantly: remove duplicate pages in the search engines by handling your own URL cannonicalization.
If they can, that's bad. Go and try it now. If you can surf your site with or without the "www" prefix, your server is probably generating duplicate content (as the same page can be reached with two different URLs), which brings down your natural search rank.
Google will try to guess which of the duplicate pages is primary -- they call this "URL cannonicalization." You're better off cannonicalizing yourself, by having your server not create duplicate content.
The right approach is to pick a URL style -- most sites opt for "with the www prefix" -- and when a visitor reaches your site via the other form, issue a 301 "permanently moved" redirect to the correct URL. Make sure this redirect is 301, not 302.
To check if you are doing it right, there are many header checking tools on the web. For example, if you type "rimmkaufman.com" into a header checker tool (this one, for example, they all do the same thing), you receive this short report
Checked URL: http://rimmkaufman.com Status: 301 Location: http://www.rimmkaufman.com/ HTTP Status Code - 301 Permanently Moved
If you're not handling this correctly, ask your web server administrator to fix it right away -- that should take just a few minutes, tops. The exact fix depends on whether you're running Apache, Microsoft, etc. You can search for 301 redirect www how to to see the various approaches.
While the fix is fast, it takes time for you to see improvements in your rankings. You will. Over time, you should see the number of indexed pages from your site in the engines cut in half (as the duplicates go away), while the rank of the remaining pages increase.
Think about other places your server may be creating duplicate content (persistent session ids in URLs, persistent tracking codes in URLs, www.yourbrand.com vs. www.yourbrand.com/index.html, etc) and come up a with a plan to remove those too, where possible. And then think about near duplicate pages, too.
You'll be better off with the search engines when each URL corresponds to a high-quality, well-written, unique page.