Last week I went to Sacramento for work, and was able to take the train to get there. It was a double bonus -- a spare the air day, and it was hecka fun.
I rode down to the Amtrak station at Jack London Square to catch an early train for the capitol. It couldn't have been easier; I locked my bike, walked into the station, used a machine to buy my ticket, then stepped out into the early morning light to wait for the train to arrive. I could have even taken my bike with me if I'd wanted, as there are racks on the lower level of each car (hear that, BART?). My boss got on in Martinez, and we watched the scenery go by until our arrival in Sacramento.
It took a bit longer than driving (2 hours vs. 1 hour, 33 minutes), but was a lot more fun and a lot less stressful (particularly coming home at commute time.) Taking into account parking and gas, it was probably cheaper than driving, too. A highly recommended way to get to Sacramento from Oakland, that gives a unique view of the Oakland waterfront, the delta, and beyond.