Why does Annie obsess about trash???
Lord, you people are dense. HAVE ANY OF YOU EVER BEEN MARRIED?!?! Have you ever seen your friends get married and divorce 10 years later?
The trash obsession has symbolic significance in the movie.
What do married couples do when they are in superficially perfect marriages? They look for trivial flaws in their situation. Anything. The thing they find cute when they get married becomes unbearable years later. Its a subconscious psychological mechanism to find excuse to doing something they don't want to do (divorce). The marriage is obviously empty, vapid, hollow. Its a loveless marriage. That is unconciously unacceptable to Annie. But when its surface appearance is "perfect", its hard to justify breaking one's vows to your partner and God, admit failure as a wife, experience economic hardship, and social loss of position.
Trash could also represent her feeling that her husband is not fulfilling his duties as husband. Many families settle on familial chores between hubby and wife. The wife cooks & the husband does the dishes and takes out the garbage.
It was probably put into the movie to lampoon vacuous yuppie couples whining about the environment, or the quality of the yardwork, rather than what really matters: the marriage.
Why on earth Soderburgh use a guy who can't make emotional contact to other women (and thus have sex), as the trigger for the failing marriage beats me. Other than a more interesting film. Once Annie does the tape, she commits marital infidelity (though not physical). Once she realizes her marriage is over, grasps the nature of Graham's dysfunction, and then proceeds to do Graham, it makes a wonderful allegory as to what was wrong with her surface perfect marriage and her decision to leave it for a "real relationship", which are two people who need, love, and actually interact with each other.
You're absolutely right, of course.