I third Ike. Best sushi in the area, hands down. You will not get the "hollywood scene" but you may run into Justin Long, Drew Barrymore or James Spader. I have seen them there in more than one occasion.
There are a couple of options for sushi and people, although the people watching is subtle at beast. Omakase room at Matsuhisa Nishimura Sushi Wa on La Cienega I don't think any of these would qualify as "fun scene" though.
It's not exactly a "scene" but Ike Sushi on the NE corner of Hollywood and Gower has phenomenal sushi, a master (Ike) behind the counter, all in a cheesy min-mall. His flash-grlled, sake-marinated Tako is preternatural.
I actually think Katana is your best bet. I find there robata-yaki good, and solid. You can walk across the street afterwards and head to skybar. Cab over there, and you are centrally located in the city.