In Google, you can easily double your core list of keywords just by adding an "s." That's because the Google algorithm treats the singular and plural forms of a given word as two different words. For example, running searches on the keywords "lifeboat" and lifeboats" both turned up the same No. 1 result, but the rest of the 10 highest-ranking results were completely different. Take advantage of this variance by being sure to include both singular and plural forms of your keywords in your Google account. However, the Yahoo! system treats singulars and plurals as the same word, so there's no point in doubling up there.