Example 1: If your URL is http://www.wigets.com/keyword1_keyword2.htm, Google will only return your page if a user searches for "keyword1_keyword2" with the underscore included. What are the chances of that happening? Slim to none.

Example 2: If your URL is http://www.wigets.com/keyword1-keyword2.htm, Google will return your page with a search for "keyword 1 keyword 2". Much more likely.

Having a hint of an idea that this was the case, I started naming web pages with dashes 3 to 4 months ago.  Unfortunately, I previously used underscores and I, unfortunately, have pages named with underscores in my web as well as many others.

For those of you who are my SEO clients and where I don't maintain your web, my recommendation is that you instruct your webmaster to start renaming pages with dashes rather than underscores and that any new pages going online use only dashes.

For those of you who are my web clients, please let me know if you want to start a page renaming program?  Changing page names will take about a minute a page plus republishing.  It is also important to have a Custom 404 page in your web explaining that page names have changed and offering a link to your site map and/or home page displaying your navigation.