I swear I saw a thread recently that claimed that California's population declined for the first time ever. I could be mistaken. A search did turn up this thread:
http://www.freerepublic.com/focus/f-news/1739400/posts
The absolute numbers of American citizens are decreasing in California. But the population in California is increasing due to immigration.
The 2006 Census estimate states that California had more of its residents move to other states than the number of residents of other states that moved there, the first time it has ever had net domestic emigration. It's population did grow between 2005 and 2006, though, due to childbirth exceeding deaths and due to immigration from foreign countries. However, if we assume that California will grow through 2010 at the same pace as it has from 2000-2006, the state will *not* gain a House seat following the next (2010) Census for the first time since it entered the union.