Can't stand Penny Lane. Anyone else?

The character is pretty representative of how "groupies" were during the 1960's and 70's. They followed bands, cheered for them, and yes...even slept with them. Even though her name escapes me at the moment, there was a groupie from the 60's that would make plaster molds of certain rock star's genitals (Jimi Hendrix comes to mind as one of them).
Penny (as revealed in the film) is only 16 years old, so yes, a bit of her is the naive schoolgirl with a crush, but part of her truly is in love with Russell. We see it all the time in life and film, where the older (and sometimes notorious/famous) man is able to charm the young, naive girl and is able to turn their crush into a full blown case of puppy love. Russell really is the one to blame as he continuously takes advantage of Penny affections, despite the fact that he is married (albiet unhappily and constantly promises her that he will leave his wife for her), and is able to take the young girl and turn her into his own personal play toy.
Like many (if not most) rock stars of the time, these women are disposable pleasures to these guys since they could roll into any town in the U.S. and find at least one woman to satisfy their carnal lust for the night. Remember that he does "sell" her to Humble Pie for $50 and a case of Heineken. This of course is to get her away from them because they will be in NYC where Russell's wife is.
I can see your opinion about her being annoying, but her naivity in believing Russell is her character flaw that adds to the overall storyline and the interpersonal relationship between William, Penny, and Russell.

How does an agent with skills like that end up an analyst?

We all have our secrets.

Penny could have been an obnoxious character, cloaked in denial about her relationship with Russell. But at the end of the day she was just a dumb young girl in love...

And Kate Hudson gave such a pitch perfect performance that I was never annoyed by her. She has an inherent, infectious likability. And a vulnerability that made me sympathise with her.

"I hope you like feminist rants because that's kind of my thing."

I'm totally with you, crimewavebetty. Look up "Manic Pixie Dream Girl" and you'll see how she epitomizes the trope. Her only purpose seems to serve the man she's goo-goo eyed over and has no inner life, except in that service.

I thought she was annoying at first. The scene that made me like her, was where she is sitting in the bus and flips the bird at a group of female high school girls. This made me realize that unlike William, she is a dropout and probably a runaway.

The point is Penny's entire top-of-the-world attitude is an act. She is vulnerable and living in a fantasy world.

She most definatly represented not only a real person but many (relatively speaking) girls. This was a life of a few of the young of the really more 70's and 80's especially, which was far more decadent and supportive of this. Arena rock was huge and music was bigger and in it's prime. A far more "live for the day" time and lifestyle. I think Penny's character was more entrenched with one person and one band than most but I saw it behind all of the forums where the autograph seekers and girls trying to get attention always were. I liked her character, it gave a clear attractive personality to the "more than a one nighter" groupies (a minority) that religiously lived their lives as close as they could to the bands and their music. Even in my small bands we had girls that followed us in the 80's. It was a certain personality and an attractive personality. We liked having them around. You have to keep in mind who wrote this movie. Crow lived this, he was there and stay's true to himself and the time and people. He's had an amazing life and wrote what he knows and lived. In the end Penny was a dreamer like lots of kids were then. She just had the balls to live the life.

Don't count on hell ever running out of room

It sounds like you're kinda intimidated by Penny Lane. Here is the thing... all the things you see in her... she tries to act like she's too cool... she tries to act like she is in control and nothing bugs her. You saw all of that correctly. She tries very hard to put up a front of being Ms. Cool. THAT is what makes her so interesting. It is interesting when she fails sometimes and doesn't get her way. It is interesting when she gets in over her head in a situation. SHE WAS NEVER AS COOL AS SHE PRETENDED TO BE. You say she seems delusional? She is delusional, but aren't we all somewhat delusional? Don't we all lie to ourselves about things in our lives? She has weaknesses just like everyone else. Her weaknesses catch up to her by the end of the movie and she crashes pretty hard. Keep in mind that you are seeing only a 2 month glimpse into the life of a young, fanciful, impetuous, somewhat shallow person who learns some tough life lessons in the movie, and will learn many more throughout her life.
Also, she sees the tour for what it is... sort of a a fake reality. A sort of a game, a big vacation, a trip to Disneyland. While on the tour, no one has to worry about the usual responsibilities of life... paying bills, working, being on time, etc... She even mentions "the real world" to William a couple times, meaning the tour was not the real world. And he doesn't understand because he is so young and honest and sincere. He doesn't know that to pretty much everyone on the tour, this is all a big game, and everyone is just having fun, playing parts, many people aren't even using their real names, like Penny. There are no consequences. So remember that the Penny you are seeing is the Tour Penny, not the Real Life Penny. It seems that at the end of the movie, she decides to take that trip to get away from Penny Lane and that fake world for a bit and get back in touch with Lady Goodman.

Can't agree with you even 1%. Penny Lane is an integral character and a catalyst for a lot of what goes on in the film. Perhaps Kate Hudson plays her as annoying and trivial, but the movie wouldn't be the same without her character, as it stands.

Nope. Only you. Damn, you have to stand alone in your opinion! How does that feel?
Seriously though, she's not perfect and that's what makes her a great character. She comes off like a force of nature at first, totally cool, steady, and then they peel off the layers one by one and she's... human! She's in love with the wrong guy and she's not delusional, he's in love with her too but he's too in love with the idea that his life "on the road" is a different thing from his "real" life that he can't reconcile his feelings for her with who he is when he's not on the road.

Anyway, not trying to convince you, it's ok if you don't like her. Everyone's entitled to their own opinion. As long as it doesn't ruin the movie for you.

For every lie I unlearn I learn something new - Ani Difranco