Jennifer Aniston, Vince Vaughn: Friends with Benefits?

We consider ourselves celebrity gossip connoisseurs.

But we've never been able to figure out the couple known as "Vaughniston." Are they together? Are they broken up? Should we refer to them as "Vinnifer" instead? Tough questions. Few answers.

In fact, just when we though that the relationship was over, this nugget comes across our desk: On the afternoon of April 21, Vince Vaughn hopped into his blue Pontiac Firebird convertible and made a familiar journey to the Hollywood Hills home of Jennifer Aniston.

Apparently the former lovebirds had lots of catching up to do... in bed!

"Vince didn't leave until 5 p.m. the next day," an eyewitness - who must've been staring at her house for 24 hours straight - tells Us Magazine.

According to friends of each actor, though, it's okay if these two got as nude as Kristine Lefebvre together. An Aniston friend says she can trust Vince, while a Vaughn source said:

"It's no big deal if he stayed over. They are friends and can be friends with benefits."

Shockingly, though, L.A.-based psychologist Ava Cadell says it's difficult for people who have been in a sexual relationship to remain friends, "so the fact that they did remain friends really shows good character and stability."

That's some seriously expert analysis, doctor. Are you gonna tell us next that it's difficult for Andy Baldwin to find true love on national television?

"It all depends on what their intentions are," says Cadell, ignoring our mockery and talking about Vince and Jen. "It's healthy, as long as they both want to do it and it feels good."

Hear that, readers? Go sleep with your ex, as long as you each want to and orgasms result from the hook-ups. (Somewhere, Kevin Federline is totally calling Britney right now.)

Anyway, let's take a look back at the ups and downs of Vaughniston's romance...
June 2005: Rumors begin circulating that The Break-Up costars are getting cozy off the set during filming, just like, well, Brangelina.

October 2005: Aniston and Vaughn are seen kissing in public and the actress visits Vince's hometown and meets his mom.

September 2006: The couple tell friends and family that they've called it quits.

Early October 2006: Vaughn is allegedly caught making out with a mystery blonde at a party in London. He later threatens to sue several tabloid newspapers that ran the story.

Late October 2006: In a last ditch effort to save the relationship, Aniston flies to London to visit Vaughn on the set of his film Fred Claus, and the couple spend several days sightseeing and catching a matinee showing of the musical Wicked.

December 2006: Aniston's rep announces that they decided to split for good following her trip to London.

February 2007: Vince attends Jen's 38th birthday at the home of Aniston's best friend, Courteney Cox, and her husband David Arquette.

March 2007: Aniston was on hand to celebrate Vaughn's 37th birthday with about 30 other close pals at West Hollywood's Sunset Tower Hotel.

April 2007: Vince spends the night at Jen's house.