Lonelygirl15 jumps the shark:
Here's the story [ on YouTube since mid-June].
There's this 16-year-old girl named Bree. She's supercute. She's also supersmart -- for fun, she reads books like Jared Diamond's Guns, Germs and Steel. She's also sheltered -- she's been homeschooled most of her life, which means she's fairly innocent and doesn't meet a lot of guys.
In other words, she's exactly the kind of girl that the young male YouTube demographic would fantasize about.
Enter Daniel. Daniel is Bree's friend. He's not really good-looking. He's kind of awkward. He's a computer geek. And Bree likes him. Holy crap. That's exactly the kind of thing that the young male YouTube demographic would fantasize about.
But, as in Moonlighting and other successful TV shows, while there is chemistry between the two main characters, there is no actual romance yet. They're "friends." Gotta have somewhere to go.
That's the basic setup, and it wasn't obvious at the start that it was fake. After all, a girl at a webcam is a girl at a webcam. How would you know if she was faking it? Had Bree just stayed put and talked, she probably could have told us anything without us knowing whether it was real or not.
But then came the plot. The producers had decided on the romance genre. Like all writers of love stories, they needed to find a blocking force, or there is no story. Boy likes girl. Girl likes boy. What could possibly keep these two lovebirds apart?
Answer: Satan.
I'm totally not kidding. ok here's where you got me. Sold! on this post.
Bree has dropped hints about her religion since she started vidblogging. What religion is it? We don't know.
..things really fell apart. Bree posted a video that played out like a soap opera. It just reeks of fakeness. Game over. Here are the problems with "I Probably Shouldn't Post This...": 1. Why are Bree and Daniel recording their fight on the webcam? Daniel actually expresses opposition to recording it -- and then allows it to happen anyway. Bree makes a lame excuse for it: "The whole world has seen everything already." This breaks a cardinal rule of serious mock-doc shooting: Never show a scene that would not plausibly be shot. Christopher Guest can (and does) break this rule, but a hoax cannot. The shaky setup forces these talented performers into some stilted acting and improvisation. Bree's bedroom suddenly looks like acting class. 2. Who edited this video? Daniel is the "computer genius" who handles the editing of Bree's videos. But they just had a fight, and it's not plausible that Daniel would then happily edit Bree's video for her -- leaving in the parts his character didn't want recorded in the first place. The editors of this show forgot a key fact: They're not supposed to exist. 3. Why did Bree post the video? Titling it "I Probably Shouldn't Post This..." isn't good enough. The Bree character actually wouldn't post this. But the producers need to get across a story point, so they have their character do something she wouldn't really do. Heartbreaking.

Is it/isn't it fake could have been an interesting running theme for the series, if only it hadn't so clearly answered the question so early. Now the only mystery is exactly who is behind it and why they're doing it.

Here's some free advice for the next hoaxters, drawn from the lonelygirl15 mistakes.
Avoid all hints of professionalism. The lighting on Bree is incredibly good, certainly ranking among the very best webcam lighting ever. The video quality is also quite good for a webcam -- almost no noise at all in the signal. Real webcam videos have flaws. And casual vidbloggers tend to be pretty inconsistent -- they don't put out a steady stream of similar-looking videos on a regular schedule. Having Bree not post for a month, or having her videos look very unpolished when Daniel isn't around to edit them would have added verisimilitude.
The story is not king...in mock-doc, the style takes story's place at the top. Not one single idea should make it into the piece if it is not 100% consistent with the central conceit. Because in this form of fiction, unlike most others, one inconsistent part can destroy the whole.
Know that you're going to be investigated. Bree's first video was posted in June. A fan website called lonelygirl15.com, purportedly created by an independent fan, appeared in July, after Bree became popular on YouTube. But YouTubers discovered that the lonelygirl15.com domain was registered on May 12, 2006 -- before the world even knew lonelygirl15 existed. Oops. The excuse offered by the fan website's apparent proprietor sounds like desperate backfilling.[said Daniel registered it] Strange, he didn't mention this intriguing fact at the start. And he would have.
YouTube is a conversation. The Bree videos so far all could have been shot within the span of one or two days. That may work financially for the production, but it wreaks havoc on verisimilitude. If the lonelygirl15 saga were real, Bree and Daniel would be far more specific in responding to the comments of other YouTubers. In fact, Bree mentioned specific YouTube denizens in her first videoblog post, but she hasn't mentioned a single YouTube user in the weeks since -- even though many users have posted response videos. She and Daniel only make vague references like "you guys were asking about..." Not good enough. If Bree and Daniel existed in real time, they'd be referencing specific comments and videos, both inside and outside YouTube.