Where the 101 and 405 meet is pretty much a hellhole. It's such a given that there will be traffic there every single day no one bothers to even report it. I went there at 9am on a saturday morning and it was a parking lot (and it wasn't because of an accident).
I live right next to the 710 where it begins in Long Beach. There are so many trucks on that freeway it's crazy. The freeway is totally torn up from the weight of all the trucks too.
There are also so many other points of congetion, 91east in the afternoon, the aptly named "Orange Crush", the east L.A. Interchange (5/110/10/101 freeway meet in one spot), and of course everyone's favorite the 405.
Although I must say, the 10 lane wide (not counting carpool lane) 5 freeway south of the 91 is a dream. It opens up so wide from 6 lanes and never has traffic, to bad its such a huge behemoth scarring OC right down the middle.