I grew up in Laguna and I'm there frequently. There are a few great casual spots: La Sirena Grill has a small downtown location and a larger location in a strip center on the south side of town - great authentic Mexican food with high quality ingredients. There's also Papa's tacos in South Laguan on the PCH for amazing fish tacos but rude owners and high prices. In the middle of town is Taco Loco. It's a favorite with locals and tourists for things like blackened calamari/shrimp/lobster tacos. I don't love the food but it's solid and the location is great for people watching.
Another local spot with very good food is Cafe Vienna in South Laguna - German food. The owner is a German immigrant that recently sold his original restaurant downtown after 18 years. They only serve dinner in the summer, but it's very, very good and very reasonable. They do breakfast and lunch every day.
The Montage restaurants are very good, and there's also Splashes at the Surf and Sand hotel. It's located right on the beach and has a great view. Finally, K'ya on the roof of the Case del Camino hotel has an amazing view and is a nice spot for drinks and appetizers.
Laguna is Orange county--south county to be exact. You will be travelling mostly on PCH-- there is great scenery and nitelife. Laguna has lots of smallish pubs and interesting restaurants. Further south is Dana Point and San Clemente. I like Salt Creek Grille in South Laguna for steaks, drinks in the nice bar, the place is gorgeous--all done in California Craftsman, fire pits outside. Also you have the resort restaurants like the one at the Montage-- I think its called the Loft. For casual, you can go wrong at Ruby's for a great burger. I know these are popular places, I am sure "locals" know more... I vacation there from L.A, so they're great for me. Have fun- its so beautiful there!