If the city isn't designed for shared transit, even a small trip is going to be awful. SuperShuttle, which picks up 4-5 groups at a time from airports and doesn't use a fixed route, can still add hours to your trip home in LA.

On the other hand, I've used airport busses between transit hubs in cities where everyone takes the subway and it was really quite nice. Better if I ever figure out luggage delivery, of course.