Kurt Peters, the editor of Internet Retailer Magazine, said today that the top 100 online merchants account for over half (53%) of total online sales. Online, merchants are starting to reach offline levels, where the top 100 retail stores account for 63% of offline retail sales.

The folks at Google posted some additions and changes over at their Inside Adwords blog:

• New sign-up wizard – a simplified process for you to add new campaigns or Ad Groups to your account and for new advertisers to sign up for AdWords.
• Updated Learning Center – participants of our Google Advertising Professionals program know that this is the place to find in-depth lessons on every aspect of AdWords. Now you’ll find text-based lessons in addition to the current Flash presentations.
• Find / Edit Ad Text Tool – locate and edit your ads across multiple campaigns quickly and easily. You can find it in the ‘Tools’ section of your AdWords account.

Good news for those of you running paid search engine marketing campaigns—average keyword prices fell 15% in May to $1.66 according to the Fathom Online Keyword Price Index. The drop comes on the heels on an 11% rise in keyword prices in April.

Leading the price decrease were mortgage-related terms which fell 30%. Were it not for the mortgage-related terms, overall keyword prices would have only fallen 3.3%.

If you’re a web retailer, one of the most important metrics for you is your conversion rate, or the rate at which your site converts browsers into purchasers. I recently found a site called Conversion Chronicles that contains in-depth information on conversion rates.

While the site breaks down average conversion rates for each industry, the average conversion rate for all sites is 2.3% and varies widely among verticals. If your site isn’t achieving the average conversion rate for your vertical, you should look at the design and usability of the site, as well as pricing and merchandising. It also would pay to examine your search engine marketing strategy‚Äîperhaps you’re targeting the wrong keywords.

Today, Google launched a new service for webmasters to submit their web sites to Google. The service is free to all. Google said webmasters can provide information about all their existing web pages, prioritize the pages they want crawled first, and tell Google when pages are updated so that it can index new content faster.

The service, called Google Sitemaps, will not replace current crawl technology, does not guarantee that a site will be included in the Google index, and will not affect a site’s rankings.

Google and Yahoo have both recently reported record revenues last quarter, spurred on partly by the growth of search engine marketing. According to Safa Rashtcy, a senior analyst at investment bank Piper Jaffray, search revenues will increase by a staggering $18 billion over the next five years. Projected revenues are expected to surpass $10 billion in 2006, $13 billion in 2007, $16 billion in 2008, and $19 billion in 2009. By the end of the decade, revenues generated by search are projected to be in the $25 billion range.