Robin HoodThere will be plenty of opportunities this summer to learn whether movie stars still exist.

Well, they exist, but do they still matter at the box office? Conventional wisdom in Hollywood has it that stars don't matter anymore, that moviegoers are drawn to the theater not by stars but by pre-sold concepts (sequels, adaptations of familiar titles, special effects showcases, simple horror premises, family-friendly animation, or anything requiring 3-D glasses). Star paychecks are dwindling, since even once-bankable A-listers have been faltering with mainstream moviegoers.

This summer, several top stars who've gone hit-less in recent years will get a chance to prove they can still sell tickets. (First up: Russell Crowe, whose dry spell has lasted three years, in this Friday's 'Robin Hood.') Almost all of these stars are falling back on traditional action heroics to revive their careers; even Will Ferrell's movie is a buddy-cop comedy. (Notable exception: Julia Roberts, who's never had to karate-chop a bad guy and isn't about to start now, is going the chick-flick route.)

Can they pull it off? After the jump, we handicap the summer comeback vehicles of eight A-listers. Cross your fingers.