Career Resurrection: The widely lauded movie is credited with completely restoring Affleck's credibility as an actor, as well as showing his good promise as a director. It also proved that Gone Baby Gone wasn't a fluke.
Fake Irish: Averted in some notable cases (e.g. Ben Affleck has Irish ancestry, which is expanded into Doug's character, and Slaine is outspokenly Irish-American and it is seen in his performance as Gloansy), but mostly played straight.
The bank manager from the opening scene is Mr. Andrews from Titanic. Also, you might know Fergie the Florist as Roland Tembo from The Lost World: Jurassic Park, or as Kobayashi from The Usual Suspects. And one of the cops investigating the crimes is the Man in Black from LOST. And for those who saw Gone Baby Gone, Affleck's directorial debut, Bubba reappears as Gloansy.
Those Two Actors: Titus Welliver and Slaine were in the previous film that Ben Affleck directed, Gone Baby Gone, which included Ben's brother Casey. Welliver and Victor Garber (Claire's boss) would also appear in Affleck's next film Argo.