There are some scenes of character being nude. No genitals are shown, but they show the characters' buttocks.
Dexter and Emma sleep together the day they meet, and they kiss, grope, and strip down to their underwear, but then decide not to have sex out of embarrasment. They instead cuddle the rest of the night. It's implied they live together for some time, although they never have sex.
When away from Emma, it is heavily implied Dexter has a very active sex life, and he is seen flirting and acting provacatively with several women. A one night stand is seen completely naked (from the backside) as she balances on his bed post. He later works for a TV show that features women dancing in tight, revealing clothing
Anne Hathaway jumps naked to skinny dip and her full frontal nudity Is briefly shown
During a call there Is a fully nude women but only from rear
Dialogue tells us that Emma and Dexter did have sex once, but the scene is not shown since it doesn't take place on the "one day" July 15th. Emma and Ian move in together for a very long time, and it is implied Dexter has many women during this time.
Dexter's first wife cheats on him. We see her sitting on a bed in a bathrobe, with a man wrapped in a towel behind her.
Other dialogue and references are made throughout the movie.