An interesting article, if a bit dated. Here is one that is a little more current - written in the middle of the current recession, in fact - that seems to indicate that California's economy is recovering and has the potential to come out well ahead. One of the things it says about immigrants, and it really doesn't distinguish between illegals and others, because there really isn't any (IMHO) is that "California's economy cannot wait or depend solely on the next round of college graduates. That means that California must remain an attractive and welcoming state—for workers and their families from other states and countries. Most jobs in California will be filled by people born and educated here. There is broad agreement including the recommendations of the Governor's Committee on Education Excellence that all of the state's children, but especially those at risk, need a good education through high school and that will require attention to both resources and reform. Filling the replacement jobs will require an upgrade in the skills and training of existing workers. Giving all students a better education is a critical goal but 80% of the workforce in ten years is already in the workforce today. That means California needs an education/training strategy that can reach existing workers who are mostly adults with families and work schedules. Given the large role that immigration contributes to California's recent and near-term workforce growth, the replacement worker challenge will require attention to expansion of ESL opportunities for adults combined with programs that allow people who are working to upgrade their skills toward targeted job opportunities."

In its usual timely manner, FactCheck.org just did a study on immigration, illegal and otherwise and employment and concluded that immigration does not adversely effect US citizen employment.