Just finished completing my California state income taxes for the first time after moving here from Maryland in spring 2008. Although my marginal tax rate (on my last $ of income) is higher in California (9.3% vs. 7.6% in MD), my total tax bill is about $2000 less in California than I paid on comparable income in Maryland in 2007. (My wife and I had a combined AGI in both years of around $150,000).
This the result of California's very progressive income tax (low tax rates at lower income levels), whereas Maryland's income tax is nearly a flat rate. Interestingly, both state's just increased income taxes. California's tax increase was across the board, whereas Maryland just increased tax rates on the highest incomes, making their new tax code more like California.
My rough estimate of the break even point between the two states is between $200k and $250k(for married couple filing jointly). So, if you earn less than $200,000 per year, you will pay less income tax in California; but very high income people will pay more in California. Of course, this is a comparison of two high tax states. I doubt my taxes would have gone down if I were to move from most other states.
The most recent tax increases will boost my CA income tax bill by about $1000 (assuming the 0.5% increase and the loss of $420 in child tax credits). It reduces my California advantage, but my family is still paying less here than on the east coast.