Tuesday

Caught in the Act!

06/30/2009 at 06:00 AM EDT

• Beyoncé and Jay-Z, double-dating with Gwyneth Paltrow and Chris Martin at Madeo Restaurant in Beverly Hills. The couples met for dinner after the BET Awards and were "definitely having a good time and laughing," an onlooker tells us. At one point, the group switched seats so the ladies could sit next to each other in the booth while the guys sat on the outside.

• Meanwhile, also at Madeo, Matt Damon and wife Luciana were eating with Jeremy Piven and a group of 10 friends. "Lucy was sitting next to another woman, chatting it up," the onlooker tells us. The whole group toasted, raising their wine glasses at one point. Meanwhile, Damon ate pasta and Piven opted for a veal dish.

• Megan Fox and on-again beau Brian Austin Green, attending the 7 p.m. performance of Cirque du Soleil's Mystère at Las Vegas's Treasure Island Hotel and Casino. Accompanied by the actress's sister and her boyfriend, the group arrived via a black stretch limo and stepped into the theater just as the show began. Fox and her friends ate popcorn through the performance, then headed to dinner at Mandalay Bay's Red Square restaurant.

• Rihanna, waiting in an Escalade with tinted windows until her booth was ready at Beverly Hills restaurant Kate Mantilini. Accompanied by three women, the R&B star sported a black blazer, tiny jean shorts and leather boots and looked "gorgeous in person," an onlooker says. The group sat in their booth for about an hour, eating rotisserie chicken and sipping on bottled water.

• Mariah Carey and hubby Nick Cannon, partying at The Eldridge in New York as Cannon played deejay for the evening. "They were so cute," a fellow reveler tells us, adding that the happy duo sipped champagne during their evening out.

• By REAGAN ALEXANDER, JENNIFER GARCIA, MARK GRAY and LESLEY MESSER

Want to see where the celebrity action goes down? Tour all the Celebrity Hot Spots.

Monday's Couples Watch >