Director/writer/actor Albert Brooks asked Nancy Reagan (who used to act under the name Nancy Reagan) to play the part of his mother. Nancy really wanted to come out of acting retirement to play the role, but declined because she couldn't bear to be away from husband and former president Ronald Reagan, suffering from Alzheimer's disease. Also on Brooks' list of former actresses to play his mother was Doris Day, but she showed no interest in coming out of acting retirement. Brooks is an old friend of actress/writer Carrie Fisher, and he knew her famous mother (Debbie Reynolds) through her. (Debbie used to try to pair Albert and Carrie off for marriage.) Brooks was looking for a big-name actress from the past and called Fisher to see if she thought her mother would accept the role. Fisher said yes, as did Reynolds.
Rob Morrow's (Jeff) hairstyle changes slightly between shots when he visits his mother; when he appears outside of the house (after storming out following an argument with his brother) his bangs are longer and 'up' whereas in the previous shots they were shorter and down on his forehead.
John is driving out of San Francisco over the Golden Gate Bridge supposedly in the evening. However, traffic is heavy going in while outbound traffic is light, indicating that it is actually the morning commute.
When John is reading his mothers transcript of the story she wrote in her youth we see that she has misspelled the name of the Whitman's candy company as Whittman.
Lawyer:
Now this being your second divorce, Mr. Henderson, I'm sure you're familiar with the procedure, but your wife, uh... ex-wife, should know it would be wise not to leave the state for a few weeks until it's finalized.
Karen Henderson: I'm not planning to leave the state.