I don't care how sophisticated and full to overflowing with snark a 16-year-old is, the scene depicted in the first five minutes or so of this film is unbelievable and has no relation to reality. A 16-year-old girl does not openly purchase a home pregnancy test while bantering with a convenience store's (which didn't look like any convenience store I've ever been in) male clerk, go to the store's bathroom and perform the test, then discuss the result in more "smart" banter with the clerk in front of another customer. Never happen.
There's another scene, near the film's end, where Juno's boyfriend (Michael Cera) somehow knows, without being told, that she's in labor, and rushes from his track meet to comfort her with some post-partum cuddling. At the end of the film, they're sitting in front of his perfectly landscaped house, playing a guitar duo. Awwww. If the film had any courage, it would admit that Cera wanted to have sex with Juno and discard her. That's what most boys (and men, too) want. But the whole film operates like TV. It wants to make the audience feel good about themselves and others, so it lies to them.
Juno is like a slightly dirty pastiche of one of those cautionary ABC Afternoon Specials and a "very special, unforgettable" episode of The Gilmore Girls where Rory discovers she's pregnant. Juno even has a bespectacled, female Asian friend, just like The Gilmore Girls' Rory.
Juno is cliched, dull, predictable and oozes with calculated, canned whimsy. Bleccch!