Franny's Mother, played by Joanna Gleason, sings very badly in the movie and is asked numerous times by her daughter not to sing. In fact, Gleason has a very good singing voice and has appeared in several Broadway musicals, including "Into the Woods".
In an early scene in Matthew McConaughey's office, he indicates a framed picture of his "sister". The prop is actually a picture of associate producer and choreographer Anne Fletcher, who had a scene in the movie that was cut.
At the first wedding, Jennifer Lopez's character Maria comforts the bride by complimenting her great thighs. This may be a small reference to the huge media focus on Jen's "big" thighs when she first began her singing career.