As a blog owner, you should know which search engines are used the most so you can decide how much time and worry to spend on each one. According to the table below (plucked from Hitwise.com), Google is way ahead of all the others but is less than 3/4 of the total.

Hitwise Chart of Most Popular Search Engine November 2008

Looking at these stats, I would place Google as first priority, Yahoo as second priority, then I would lump MSN and Ask.com with other sites not listed here such as Metacrawler, Webcrawler, Dogpile and IxQuick. The reality is that if you please Google and Yahoo….sooner or later the other search engines will list your website anyways.