I thought from the reviews that this film might be awful, but it's LOL funny at points and the story is really cute. Zack and Miri are long time friends and housemates who decide to make a porno (and therefore, have sex) to make some money to pay the bills. But inevitably they can't keep emotions out of it. So really it's a bit of a chick flick in disguise- for people who don't do chick flicks. Nice to see Jason Mewes in it, who is not starring as Jay in this film but is really funny anyway.
I don't live with my parents, but agree with earlier reviewer that if you do it's one to watch when they are out, or with the sound down.
Give this film a chance, it's a nice story and it has some genuinely funny moments.