Juno/WMG

Juno is an older version of Haley from Hard Candy.
She dresses in red, has a noose scene (what better way to off herself than the way she offed the pedophile, to balance the universe), and sees "meat swords" whenever guys run by. Plus, we never found out Haley's real name, and both characters are clearly very dominating and insightful. If nothing else this makes the movie much funnier.

Juno is a younger version of Haley from Hard Candy.
As an alternative to to one above, Haley's the older version (she could have been lying about her age), and Juno, suffering from horrible post-partum depression and traumatized by Mark Loring's inappropriate feelings towards her, decides to go after pedophiles.
 * Or, if you're one of the three people who saw it, Tracey from the The Tracey Fragments could fill in for Juno here. She's obviously on the verge of going Axe Crazy.

Mark is Paulie Bleeker's real father.
He had a relationship with Paulie's mom before she married, anything from a fairly serious one which was broken off to a one-night stand, before Paulie's "dad" entered the picture...

Mark and Paulie are of course Michael and George Michael from Arrested Development
Michael and George Michael took a wrong turn at Albuquerque on the way to Cabo in the series finale and wound up in ....Montana was it? They decided to take on new identities and went there separate ways. The rest of the Bluths, desperate for Michael's help, sent a certain reporter to track them down...
 * Minnesota, actually. Mark and Vanessa live in St. Cloud.

Haley is Juno's M-t-F daughter.
Juno's daughter started transitioning early in life, and naturally resembling Juno, resembled her even more while in the process of transitioning/after completing the transition.
 * Daughter, thank you.
 * My apologies. I've edited the entry.

Juno is Shadowcat before her mutant powers develop
Her father is of course related to J Jonah Jameson.

Paulie and Juno are Shadowcat's parents
It's well-established that Kitty Pryde is Jewish, and Paulie probably is as well (see Ambiguously Jewish example). Juno will probably convert after they get married. They'll be forced to change their family name to "Pryde" to protect themselves when Juno's first baby turns out to be a mutant and tries to get revenge on Juno for abandoning her. Kitty will join the X-Men to get the training that she needs to defeat her evil sister.

Juno is Junie B. Jones, all grown up
It's totally true. Juno went by Junie when she was a kid and took the name MacGuff when her mother remarried. Even as a child she displayed the same penchant for quirkiness, making up language, pulling off Zany Schemes, and being independent.

Paulie was going to bring condoms, but chose to forget about them to impress Juno.
Okay, the wording on that's a little awkward (seen this movie five times and I still can't figure out whose house they did it at). But long story short: Paulie knew that Juno wanted to have sex that night. Being the good part-time lover/full-time friend he is, he was going to bring the appropriate contraceptives, but figured Juno would like it if he didn't. She would probably have teased him if he did bring them (what kind of virgin weenie is into being safe?) Word of God states that Juno was not a virgin when she had sex with Paulie. Having it like, seven times with another guy might have given her the confidence that falling pregnant would not happen just one time with a newbie. Obviously, that plan failed miserably. It would also explain why the "But We Used a Condom" counter argument was so weirdly averted.
 * The sex happened at Juno's house, right? In the start of the movie, Juno is standing outside drinking Sunny D, staring at the chair that she and Paulie...you know. We know she's not at Paulie's house, because she later takes that chair over to Paulie's front lawn.
 * I always assumed it was at Paulie's house. She's ataring at a chair, yes, but there's no proof that it's the chair. Although I haven't seen the movie in a while, the way I saw it was that she was walking around the neighborhood drinking Sunny D while she waited for the need to pee so she could get a test, and on her walk she spotted a yard sale, and, seeing some of the items sitting on the lawn, decided that they would be a good way to break the pregnancy to Paulie. Because, you know, that's the way Juno thinks. In my ind the yard sale lady told her that if she came by later and the chair et al hadn't been sold, she could have them as long as she had the means to get it all off the lawn. I could be crazy, though.

Juno's stepmother is the Island Matriarch from Lost.
After the events in Juno, her stepmother was called by the Island, then still under the control of Jacob, who recognized his own stepmother. But during her "accidental" travel to the island, she was caught in a time travel phenomenon and ended up in the distant past, where she had to take up the position of keeper of the Island. She went insane because of missing her husband and daughter and stepdaughter, and because of not having pet dogs. When she found the pregnant mother if Jacob and MIB in 'Across the Sea' it was all too much because of the memories it brought back, and she finally totally snapped, with the consequences we all know.

Mark was actually the father of Juno's child
Mark and Juno were having a inappropriate relationship long before they 'first meet', when she decided against abortion she told mark she was planing on coming out in the open about them. Mark knowing his barren wife wanted kids and than his dreams of rockdom would never happen if came out he was an Ephebophile suggested the adoption ruse as cover. Juno seems like enough of an tool to hook up with Paulie simply for Plausible Deniability.

Vanessa was a pedophile.
Such a cynic, aren't I?