Those positive feelings about this year’s booming box office grosses may soon sour. And that spells trouble for movie theater companies including Regal, Cinemark, and AMC. Coming into summer, 2009’s year-to-date was half a billion dollars ahead of last year’s. But this past weekend was the 3rd in a row to fall short of 2008: ticket buyers spent only $138.3 million for the opening of The Taking Of Pelham 123 as well as more Hangover and Up. But that’s down a whopping 23.1% from last year when The Incredible Hulk opened. Lazard Capital Markets’ Barton Crockett writes that next weekend, which includes the premiere of The Proposal which Disney thinks will do well, still will fall 10% behind last year when Get Smart premiered. And the analyst says that even the following weekend’s debut of Transformers 2 should run 14.8% behind the 26th weekend of 2008 which included Wall-E. (Jeez, even with Transformers 2 expected to make $160M-$175M over its first 5 days?) Although year-to-date sales are running 10.7% ahead of last year (not counting inflation and higher ticket prices), Merriman Curhan Ford’s Eric Wold is cautioning entertainment investors to “stay on the sidelines” until prospects for the rest of 2009 become clearer.