I took PCH up from L.A. one year ago. Make sure to visit the cafe in Pismo Beach with the clam chowder. Shoreline Cafe or something. Hit up breakfast at Zachary's in Santa Cruz too.
If you're being strict about staying on PCH, when you hit the Oxnard area, it will turn into Oxnard Blvd. It's just like a regular street and there's nothing to see and it's quite a bit of a drive to finally get back on the coast in Malibu. You can skip this by staying on the 101, but you'll miss a large part of the Malibu portion of the drive.
Before that (if you're being strict on staying on PCH), you will actually get off the freeway before that and pass through small towns that are mainly agriculture (you also pass a huge air force base). Don't miss this because it becomes miles of strawberry fields and the smell is amazing.
Once you get past Santa Monica and the like, you may just want to hop on the 405 as PCH will become a traffic-clogged street down near Palos Verdes. I don't even know where it continues down past Orange County though.
Good luck.