How accurate is the CBO?

Recently I ran into fierce debate over that accuracy of the Congressional Budget Offices ability to accurately provide budget analysis and cost estimates. Today they are providing a report on Obama’s proposed 2011 budget that if accurate within 10 years will drive the US back into the stone age.

“President Obama’s fiscal 2011 budget will generate nearly $10 trillion in cumulative budget deficits over the next 10 years, $1.2 trillion more than the administration projected, and raise the federal debt to 90 percent of the nation’s economic output by 2020, the Congressional Budget Office reported Thursday”
http://www.washingtontimes.com/news/2010/mar/26/cbos-2020-vision-debt-will-rise-to-90-of-gdp/

Before I get caught up in all the hand waving, anybody here an expert on this stuff?? This one more time I hope they are wrong.