Ohhh in porn
Pornographic ohhhs are particularly distinctive, being long, drawn out and just loud enough to let your other housemates/neighbours know that you don't have an actual sex life of your own.
Ohhh in real life
Ohhh is generally a sign that you're getting something very, very right. It should on no account be confused with Oh.
Ohhh from idiots
This is a sign that somebody has finally figured something out....