For the year 2009, the Top Search Engines are :

• Google : With 73.66% search conducted on it.
• Yahoo : With 15.55% search conducted,
• MSN : with 5.64% search conducted and
• ASK : with 3.81% search conducted on it.

One thing is sure, one cannot underestimate any of them, neither google, nor ASK. ASK definetly has less search going on for it but each search engine has its loyal customer base; and as a optimizer, we simply cannot ignore or avoid it.
Lets see how the Top 3 search engines differ when optimizing:

• Google has its own Pagerank feature, neither yahoo nor MSN can boast of this. Though, yahoo has come up with its own pagerank tool a few years ago, this feature was disabled shortly.

• One of the most important differences in MSN & Yahoo is that, they rely heavily on metatags. The keywords & Description must be unique for every page. The same cannot be said true for Google.

• It is hardly surprising that keywords are the most important item for MSN. While Yahoo lays emphasis on Keyword Density (Ratio between the total number of keywords and non-keywords used in the body text, title, link-anchor text, and meta tags). But never do the mistake of stuffing your keywords in the page, for this will cause Google to Blacklist your website (Google after all is the Top Search Engine!!). One has to be very tactful with keywords.

• The most important difference between Yahoo & Google is the way keywords are placed in url & Title. If you get this right, expect a top 10 place in Yahoo.

• Google pays more importance to backlinks, more your site is popular with other sites, its popularity & Pagerank in Google improves. The same is not so true with yahoo & MSN.

• Most of the Search Engines give priority to Old domains. Older the domain, more the search engines will love it.