Does Hollywood need to go Back to School ? This summer is on track to equal, and maybe even surpass, the B.O. record. To date, tallies are running even with last year's summer numbers at $3.6 billion. And it could eclipse the record-breaking $4.3 billion earned in summer 2008.a So in theory, studio executives have plenty to learn by studying what worked this summer -- and what didn't. But, in fact, Hollywood has tried some daring experiments with the summer formula this year and the results are inconclusive. There were whopping successes and embarrassing failures, and execs are scratching their heads to figure out why some succeeded and others didn't. There are plenty of questions to be raised from these numbers. •Does a May bow assure longer playing times? A few years ago, the studios opened three blockbuster titles in May: The third editions of "Spider-Man," "Pirates" and "Shrek," all had great bows, followed by long shelf lives. This year,