To me, PG is action cartoon violence, the next step past a kid's show, like say, Batman. You should also be able to mildly cuss (nothing they wouldn't have said on early Simpsons episodes that is). Even very dark, almost too disturbing for little kids plot lines, like The Incredibles (A super villain killing all the super heroes so he can become the only Hero in the world). But more often than not, the meaning of G and PG are blurred, and those "PG" movies are just marketed as PG because G won't fool 10 year olds who don't want to go see it.unite! You have nothing to lose but your chocolate chips!
On the subject of the PG rating, I actually think it DOES serve a purpose, but it's lost it's context in recent years, because, let's be honest, when's the last time a theatrical movie had an actual G rating?
Here's my take on the subject: PG is just what it is, it's a step up above G, but not quite PG-13. There are really two kinds of PG movies, there are PG movies that are specifically targeted at kids and families, then there are PG movies that are for adults. PG movies for kids are PG because it's a kids movie, whether it's a cartoon, CGI, etc, the characters and the storyline is conceived for kids, however, why is it PG? It may have some mild swearing in it, or there may be some situations in the movie that are "perilous" and "intense" that might bother younger kids and even frighten them, hence "Parental Guidence Suggested". That's essentially when a movie like Pee-wee's Big Adventure is PG: it's a kid's movie, because Pee-wee USED to be a kiddie icon (though unfortunately because of his not being able to master his domain scandal, it's the opposite of how people interpretate the Muppets as supposed to be for kids only, Pee-wee is now seen as being for adults only), however, there are some rather freaky scenes throughout the movie (but would you expect any less from Tim Burton, lol?), not to mention a brief scene of Twisted Sister shooting a MV for "Burn in H e l l", while the word isn't used as a swear, it's still a "bad word" either way. So you can see why a movie kid's movie like that would be "PG".
Now getting to the subject of PG movies for adults, these are essentially PG because of lack of more "adult" content and because it usually has tame language... so why is it targeted at adults? Mainly because the storyline might be like a "slice-of-life" story, and whatnot that would be boring for kids, with no fun, colorful, wacky characters.
Now, you take a movie like Speed Racer, cussing, big violence, Spritle flips someone off for a half second. THAT'S what i call PG... even the Shrek films. Personally, I miss the first TMNT movie... a LOT of martial arts action, Raph cussed (in character, I might add) a couple times, and it was a very dark plot line. Where as the newer TMNT movie seemed like it was a G movie. The violence was basically the same as a TV Y7 cartoon, no cussing, it wasn't all that dark... and pretty much kids slightly younger than 7 went to see it (trust me... I saw it opening weekend). Kid leaning PG-13 movies are more what PG movies should be like, while adult PG-13 stuff is bordering slightly, but not quite on R.
But again, there's no call for some of the kid's movies I've seen to be PG. I still find it a scam so parents will have to take their kids to one of those...