Holding the bag will be the investors in these mortgages. Investors funded the houses and refinancing boom and America’s big spending spree: Pension funds, hedge funds, and other investors who own mortgage backed securities, collaterialized mortgage obligations, and first and second deeds of trust, and bonds in government sponsored enterprises, and banks who directly hold these loans (i.e. Golden West Financial). Also stock holders in Fannie Mae, Freddie Mac, and Ginnie Mae, for mortgages under the “conventional” limit.
There doesn’t appear to be any data on who holds these investments. It’s not tracked, as far as I know.
The housing bubble collapse will wipe out some individual homeowners completely, and the general economy will suffer right along with them. Loan defaults will wipe out investors, pension funds, hedge funds. I think the fall out could be huge, but again, without the data regarding who’s holding what, we won’t know who’s swimming naked until the tide goes out (gotta love that quote!).