I first saw this film as a college student in an Italian Cinema class. I was impressed then, and recently saw it again and was touched anew by these characters.
Then I noted that Martin Scorsese, in his documentary about Italian film on Turner Movies Classics ("My Voyage to Italy") names this film as a huge inspiration for his film "Mean Streets" -- and I felt totally exonerated that I had always placed this film up there with La Strada, 8 1/2, La Dolce Vita, and Amarcord.
Scorsese sets the record straight about how these characters are successfully fleshed out -- including Moraldo, the Fellini autobiographical character. This is a film of simple beauty, and while it may lack the complex allegorical meanings of La Dolce Vita and 8 1/2, the story more than delivers in its straight forward approach to story telling.
Forget Diner (a decent movie), Slackers, Clerks, and any other "slacker/loafer" movie; I Vitelloni transcends the genre -- and it is a true classic.
Rent this film - it will not let you down.