Traffic and transportation are hard problems, but this area seems to always choose terrible solutions for either of them.
Caltrain is pretty horrible schedule wise.
My experience with the Muni system in the city is that it is less than dependable. Frequent backups, delays or even skipped trains seem to be normal. When I have to use the Muni I basically leave work 10-15 minutes earlier than when I first started this job just because I can rely on the unreliability of the Muni system.
At least as a person without children, the need for and experience of using a car is simply a matter of where I live and work (and for the weekends, where my friends live). When I lived in Pasadena, commuted to Irvine 3x a week, and didn't have a personal car, yes, life was miserable. When I lived in Venice Beach and drove downtown for work, the tedious, heavily trafficked freeway commute exhausted me by mid-week.
Also, for what it's worth, greater Los Angeles has the highest average density of US urban areas by a pretty healthy margin. Yes, it's denser than the New York or San Francisco urbanized areas. And LA's decentralized commercial districts make it a prime candidate for an efficient, extensive public transit network [1]; there's just heaps of toxic cultural momentum to overcome in order to restore that former feature to our metropolis.
[1]: http://humantransit.org/2010/03/los-angeles-the-transit-metr...
In a big and dense city you would most likely be jammed in traffic while you could just walk to the nearest underground station or tram/bus stop and take the next transit towards the right direction. And the latter is what people do in places where taking the car is not a requirement and where the densities support public transit. In most American cities the densities are laughably sparse, and taking a personal car makes sense.
In LA or Valley it would be a joke not to drive. In NY or London it would be a joke to try to drive.