Amtrak California's Pacific Surfliner route runs from San Diego to San Luis Obispo and serves as a major link between San Diego's Santa Fe Depot and Union Station in Los Angeles. Surfliner trains are made up of
double-decker cars similar in size to the Superliners found on Amtrak's long-haul routes but configured almost exclusively as coaches.
The cost of a basic ticket starts at around $30, reflecting the subsidies inherent in the Amtrak California partnership. For about $15 more than the Coach fare, though, passengers can upgrade to Pacific Business Class, and I recommend it; the perks of the Business-class car include roomier seats with tables reminiscent of the East Coast's Acela Business Class, power outlets for every seat, and self-serve coffee and snacks on both levels. For passengers in Coach, there is also Cafe Car on the train that sells snacks and beverages.
In my opinion, the Pacific Surfliner is an outstanding train. The extremely low cost of the trip combined with the comfort and convenience of being able to read or work en route without worrying about traffic makes this the way to get to Los Angeles. If you're planning to travel during peak times, though, be aware that the standard Coach seats are unreserved, which means you are not necessarily guaranteed a seat. (Pacific Business Class tickets do guarantee seating.)
Traveling from San Diego to Los Angeles takes about two and a half hours on the Pacific Surfliner, with service offered between those two stations at most times throughout the day. The entire route from San Diego to San Luis Obispo takes much longer--a total of around eight and a half hours--because of the many stops along the way and is offered only once per day without requiring a transfer to a connector bus or another Amtrak route.
For the non-commuter, probably the best use of the Pacific Surfliner is as a means to reach Los Angeles Union Station, the southern endpoint for Amtrak's famed Coast Starlight route. Spontaneous Tourists will appreciate the opportunities afforded them by flying into what may be cheaper airports in Orange County or San Diego and reaching Los Angeles by rail rather than flying directly to LAX--not always a savings, but always worth considering.