I lived in LA all my life up to four years, but unfortunately I was not into triathlons back then. Living in Hollywood Hills will definitely give you some challenging hills to climb, but since you are from the Bay area you should do quite fine. Same goes for the running. If you don't mind the drive getting down to beach ( I prefer Huntington) for a run is a great way to change scenary, but I wouldn't recommend it for a bike ride as you are constantly weaving in and out of pedestrian traffic and sand is being blown in your face.

One disadvante to living in LA is that your workouts will be very short loops that you need to repeat constantly, unless you want to drive somewhere. There is a park in San Dimas called Bonelli Park (next to Raging Waters)(about (30 minutes from HH) great place to run/ ride. Run loop is 7 miles and I think the bike look is 10 miles.

Have no clue about the swimming though.

biking: I live in Pasadena and I found the San Gabriel River bike path to be the best and safest ride for my training. Griffith Park in Glendale is also very nice to ride around and run (Team in Training runs there and post mile markers)

For swimming - I use my 24Hr Fitness club to do laps in their little pool. It's mind numbing but that's as much as I can afford... Malibu's Zuma beach is a popular beach for Open Water swims - you can see a few teams show up on Saturday mornings near the last lifeguard tower (I think #12 or 14).