これはイディオムです。意味はusually, as a rule, most of the time, in most casesとなります。次の英文を読んでみましょう。For the first time in years, more Americans than not(=most Americans) say the country is headed in the right direction, a sign that Barack Obama has used the first 100 days of his presidency to lift the public's mood and inspire hopes for a brighter future. ややひねった表現も基礎が出来ていればまったく問題はありません。more...than notの形を覚えておきましょう。
http://www.youtube.com/watch?v=WDj2Q7us5D0 3:46 more likely to run than not
http://www.youtube.com/watch?v=zypDx6a-PZU 1:36 more often than not
http://www.youtube.com/watch?v=9t-TSj-1i6o 4:42 more americans than not
http://www.youtube.com/watch?v=pnqSy_DUwAw 6:23 more often than not
http://www.youtube.com/watch?v=0B-Xlh-Dpz4&feature=feedu 0:52 so often, more often than not
http://www.youtube.com/watch?v=syuJ7F2nuCo 1:20 more likely than not
http://www.youtube.com/watch?v=T8KJGtMGMSY&feature=related 4:05 more often than not
http://www.youtube.com/watch?v=pMd17XHEbsE 0:29 it happens more often than not. この現象はよくあることだ。
