By Michelle Tan
October 15, 2007 12:00 PM

The newest drinking game to hit Hollywood? Call it the Drew Barrymore-Justin Long Smooch & Sip. The rules are simple: If you spot the free-spirited actress and the man from TV’s Mac ads getting cozy at a local hot spot, fill your glasses. And when the pair starts making out—down the hatch! That’s just what happened on Sept. 3 at the L.A. sushi restaurant The Izaka-Ya by Katsu-Ya, when other diners spotted Long and Barrymore at a table enjoying each other’s company. “They were so cute together, but they kept kissing and kissing. They couldn’t stop!” says one observer. “So every time they kissed, we took another sip of wine.”

Are Barrymore and Long drunk on love? Clearly the couple—who met while working on the romantic comedy they’re currently shooting, He’s Just Not That Into You—are very into each other. Since her relationship of more than four years with drummer Fabrizio Moretti ended in January, Barrymore, 32, has been playing the field, spending time with director Spike Jonze and Scrubs star Zach Braff. But things with Long, 29, are different. “It’s very serious,” says a source. “They are constantly texting and calling each other.”

By day, the two actors show up for work alongside Into You costars Jennifer Aniston and Ben Affleck, and are professional. But after hours, they aren’t shy about their feelings. Over Labor Day weekend, the duo hit Las Vegas clubs and “were all over each other,” says a witness, and recently at West Hollywood’s Bar Lubitsch, “they were totally making out,” says an onlooker. “They looked very happy.”

At first glance Long, a self-described “huge nerd” who is best known for playing a computer in the Mac commercials and a tech geek opposite Bruce Willis in Live Free or Die Hard, and Barrymore seem like an odd couple. In fact, a few jealous guys on the Into You set were mystified. “We all think Drew is a huge catch,” says a source. “As soon as we heard that they were dating, we all thought, ‘How did he get her?'”

The answer: Long, a Fairfield, Conn., native “made [Drew] laugh—and that’s what the initial attraction was,” says a source close to Long, who split from his girlfriend, actress Kaitlin Doubleday, this summer. “With girls, his No. 1 motive is to make them laugh.” Adds Into You writer Greg Behrendt: “He’s hilarious. Drew is a gem. I hope it works out.”

Judging by Barrymore and Long’s Sept. 27 outing to L.A.’s Chateau Marmont, it’s working out just fine. “They were not even talking that much,” says a witness, “but kissing half the time.” Cheers!