Tools of Characterization
We can't help but notice how many scotches our characters drink over the course of the evening (about 22) and the fact that they smoke marijuana. The narrator claims drinking is one of the couple's "pastimes" (1.32). Robert suggests that he's a habitual drinker as well. While the marijuana is a first for Robert, it's a habit for the narrator. He tells us "Every night I smoked dope and stayed up as long as I could before I fell asleep" (2.29). What these habits say about the characters depends a lot on how individual readers feel about alcohol and marijuana use.
Getting intoxicated isn't the only habit our characters have. The woman is in the habit of writing poetry, and she and Robert have a habit of corresponding via audiotape. Unlike drugs and alcohol, poetry writing, and correspondence can easily be seen as positive habits. Unless you're the narrator, that is. He isn't quite sure he likes either of these habits, especially the correspondence.
Instead of focusing on individual habits, we can look at how all the story moves from the habitual to the spontaneous. The dinner party/slumber party is a break from the habitual for all the characters, even though they engage in some of their usual habits. By the end of the story a spirit of spontaneity has taken over, and sense that all the characters are in for new routines.
Thoughts and Opinions
The narrator's thoughts and opinions about blind people are what many readers remember most about "Cathedral." He walks a fine line between funny and offensive, and that's a memorable characteristic. Some readers might think he crosses over to the offensive side too often for comfort. In his analysis (and those of the other characters) we try to see beyond the surface, while acknowledging that the surface is important, too. The narrator's opinions about blind-people before he meets Robert help us understand the magnitude of his change. If the narrator didn't have strong opinions about the blind, his experience with Robert would probably still seem big, but not as dramatic, visible, and obvious to the reader.