Terminator 4 is going to Suck
The studio making Terminator 4, in its wisdom, has decided to shoot this film for a PG-13. And now it has signed up a rapper to act in it. I have two problems with that: 1. The only good Terminator films have been the ones rated 'R', and (with the exception of LL Cool J), most of the rappers I have seen in movies can't act:
http://www.aintitcool.com/node/3663 3
http://www.aintitcool.com/node/3663

On the other hand, ratings have been dropping in real terms; stuff that was X certificate when it was made is quite often PG now. So it might not be as bad as you think. Especially if the context is quite futuristic, which always seems to get a lower rating.
That said, the fourth 'Die Hard' was filmed as PG-13, and when I saw it I had the impression I was watching a tiger with all its teeth extracted. John McClane just isn't the same without his 'Yippy Ky Yay'.