Oddly enough, I was just reading about this, a friend mentioned it first, then I realized she was quite right.
Link
The similarities are pretty good. However Rockstar makes a huge disclaimer, in the beginning of the game, saying that any similarities b/w the characters and real life people/characters is a coincidence. Not to mention, they could have used the Novel as well for inspiration, even though it was based on the 1950s not the 40s. Minor detail however.
So if they did take a page from LA Confidential, they won't own up to it. Probably to not pay licensing fees. lol
Thanks for the link I enjoyed the article.
I think one way that L.A. Noire might try to hide it's similarities is by the fact that it is a very long game so certain plot elements take a much longer time to take shape and develop instead of things coming together quickly as they did in L.A. Confidential whick lasts all of about a little over two hours.