This is probably the best known run in the Santa Barbara area, but if you're on your way from LA to SF, it's a really fun detour, especially at night. In fact, it's actually faster to take 154 than to go 101N through Gaviota; it'll save you about 10 miles.
The asphalt quality is FANTASTIC, and in the uphill direction from Santa Barbara there are 4 passing zones.
Once you're over the pass, you can continue on 154 for about 30 miles. It dead ends into 101 again just north of Buellton.
If you want a really crazy run, you can turn right off of 154 at Los Olivos and go out Foxen Canyon road. Every time the road dead-ends, just keep turning right. Foxen Canyon Rd goes all the way to the Betteravia exit in Santa Maria. Even in the daytime it's fun and relatively low traffic.
Watch out for animals and cyclists, though. And if you see a black wagon behind you, please be courteous and pull over.