Ray Comstock tells us why duplicate content is a problem and how canonical tags can help. He explains how to implement tags on nearly every page of your Web site, and explains how tags can help prevent problems caused by duplicate content, including pagination and redirect issues.

Flight search engine Hipmunk now lets people search for and book hotels. Evidently, hotel bookings are where flight search engines make their money, according to Matthew Lynley. He tells us about the company's financial backers at Charles River Ventures, an early investor in Twitter.

Ken Burbary gives us an interesting perspective on identifying influencers. As an example Burbary points to Charlie Sheen joining Twitter and gaining 1 million followers in about 24 hours.

Rand Fishkin tells us about SEOmoz's analysis of Google's algorithmic update launched In February. He writes there's no way to tell precisely what Google changed to impact nearly 12% of queries, but the team has some ideas that contribute to the discussion. He show us how to see the "Farmer Update's Effect" on Web sites with Google Analytics.

Microsoft launched a viral contest to gain new ideas for mobile apps, and built in a way to measure interest, according to Adam Sutton. He tells us how the contest incorporated social and viral methods to help uncover the apps generating the most excitement. One grand prize winner would receive $5,000, new Windows Phone 7 device, and the app would become available as a free download for the platform.

How does the click-through rate influence the cost per click paid in adCenter, and how much influence does the quality of the landing page have on CPCs? Those questions were answered during an OMMA Global panel discussion on Tuesday in San Francisco. The Search Agents' Frank Lee led the discussion based on Marin Software's evaluation of the Bing-Yahoo alliance.

Richard Baxter explains the nuances of site architecture for SEO. He tells us how to reduce the amount of clicks from the homepage to the deepest content, and what a bad and good site architecture looks like. Keeping the site lean and clean, similar to a reporting structure at a corporation, should help site visitors find the information they seek.

Searchmetrics monitors more than 55 million domains and 25 million keywords. The company continues to track changes to the Google "Farmer Update," to monitor effects on search engine rankings. Marcus Tober provides a detailed account of the changes, and the biggest winners and losers.

Some big losers in the Google content farm update are premium AdSense publishers used by Google as case studies, such as Hub Pages and EzineArticles. Many of these sites won't bounce back -- because "the Web has evolved and the algorithm has moved beyond them," Aaron Wall wrote. He tells us why a "cleaner" click-through rate might be better than a quick hit.

A preferred advertiser list published by Facebook went into effect earlier this week. Guess who's not on it? Google AdSense. Nick O'Neill gives us the lowdown. It's still possible Google could make the list.