UPDATE [8:38 p.m.]

It now appears that collision at West Portal was worse than previously thought. Pat Gardner, Chief of Operations for the SFFD, interviewed following the collision, told reporters that 44 passengers have been transported to San Francisco hospitals. Three individuals suffered "red" or severe injuries, 20 "yellow" or moderate injuries, and 21 had "green" injuries and were described as being the "walking wounded."
Among the three individuals badly hurt were the operator, along with two passengers with possible head injuries.
Video, via CBS 5, is available here and here.
Obviously, this was a traumatic scene, and our thoughts are with the individuals and families involved and affected.
UPDATE [9:12 p.m.]
While listening to KQED, I just heard the hourly newscast. Leading off the news was this collision, meaning that the accident has made national news. The New York Times is carrying an AP story online at its website. Several other major outlets are carrying the news, including CNN and The Los Angeles Times. As they point out, this is the third major rail collision in the United States since May, the other incidents occurring in Washington, D.C., and Boston.