In Monterey Park, this is one of the most popular Dim Sum places. I'm sure you could wait an hour even on a weekday. The place is huge too. If you really want the Dim Sum experience this is the place to go.
Also, Monterey Park and the areas nearby are heavily populated by Chinese as well as some other Asian groups. The cool things is there are tons of great and fun restaurants, several video game stores and also a couple of Hong Kong movie theaters so if you want to see the latest Jackie Chan or other Hong Kong movies years before their official American release check it out!