Numbers from calculatedrisk are misleading (I’d even say inaccurate). 20% nationwide decline is the average of 50% decline in California and maybe 10% in Minnesota.
Personally I expect 50% default rate among all homes bought or refinanced in CA/AZ/NV/FL between mid-2004 and 2007. Something like 700k foreclosures in CA and 50k foreclosures in San Diego county.