I ended up seeing, "Our Idiot Brother" this weekend. While it definitely wasn't necessarily the comedy I thought it was going to be - I enjoyed it. Paul Rudd was excellent and the movie revolves more around his self-involved three sisters than it does the "idiot" brother. The character isn't so much stupid as he just sees the world in a slightly different way - which I think Rudd found a way to portray without cloyingly pandering to the audience like they sometimes do with those kinds of characters.
I hesitate to call it a dark-comedy and more like a "dramedy"... Don't know if I'd recommend making a special trip to the theater JUST for this, but if you like Rudd - it's probably worth a rental or netflix down-the-road. TJ Miller (Cloverfield, She's Out of Your League) also has a pretty funny cameo in the movie as well.
Also a warning, you pretty much get a goatse from Steve Coogan - which was... pretty gross.