The total count of host names is around 156 million (from a Netcraft report), the average sites number by hostname should be around 10, so i think the answer is something like 1 560 million.

(Note : Technorati claims that the total number of blogs is currently more than 100 million.)

the total number of websites on internet today, is over 6 billion and That number is not including blogs and websites such as myspace pages, facebook pages, or other branches off of websites.