Newspaper Web sites garnered 66.4 million unique visitors in the second quarter, a 12.2% increase compared with the same period in 2007, according to a report released Tuesday by the Newspaper Association of America.  (The number of unique visitors represent 40.2% of all Internet users.) In addition, newspaper Web site visitors generated an average of a little more than 3 billion page views per month throughout the quarter, compared with nearly 2.7 billion during the same period last year. But while newspapers continue to grow their audiences online, it’s still an open question whether digital gains can offset print losses.