Pretty amazing cast...

Inside Movies details the full cast list:

The movie, set to release Jan. 25, 2013, has a cast and story as celebrity-steeped and plot-twisty as a Robert Altman film crossed with the shameless spunkiness of Jackass. In addition to Watts and Winslet, it includes appearances by: Elizabeth Banks, Halle Berry, Kate Bosworth, Gerard Butler, Kieran Culkin, Josh Duhamel, Anna Faris, Chris Pratt, Richard Gere, Terrence Howard, Hugh Jackman, Johnny Knoxville, Chloe Moretz, Justin Long, Leslie Bibb, Liev Schreiber, Seann William Scott, Emma Stone, Jason Sudeikis, and Uma Thurman. Whoosh, that’s a mouthful. With all those actors, more than 15 writers, and several directors, including Farrelly and actress Banks herself, the movie took several years to make.

Everyone's a bit vague on the actual...uh, plot, but Screen Rant gives it a shot:

ven though the trailer doesn’t exactly spell it out, the film will consist of intertwining comedic vignettes featuring the characters we’ve seen (plus others yet unseen) that ultimately converge in some kind of way. So far we have a couple of parents with an unusual approach to home-schooling; various characters preparing for some kind of a faux Comic-Con; a company working on some kind of sex doll/robot thing; a riff on inspirational African-American sports films, and smaller bits featuring odd-pair couples in various comedic situations.