Quote from gnome:
A California friend mentioned this but was unsure. However, it doesn't seem right.... unless the bank would require a large down payment to protect its interests.
See for example (CA):
http://www.wwlaw.com/forecl.htm
Note that this article is dated 1996, but I don't think mortgage default law has changed in Ca since then (default on a mortgage loan does not require a bankruptcy declaration, I believe).
In NY, remedies beyond the subject property are not implied covenants (so, not sure what happens in practice).
You're right about the credit risk for near 100% LTV loans. However, generally, any LTV above 80% requires mortgage insurance, and some lenders require the last X% be a second mortgage. I guess the assumption is that the intangible cost (credit report) to walking is high enough to prevent individuals from doing it too often (plus, you can only do it once or so, lol) See http://ideas.repec.org/p/nbr/nberwo/5184.html
GSE-conforming loans (cheaper than subprime or jumbo) require 80% LTV and they insure the MBS investor against credit risk (but not prepayment risk) - so I'm surprised that most states would have recourse. Also, a lot of the mortgage pricing literature talks about the "embedded put option" in mortgages so, again, strange (see http://papers.ssrn.com/sol3/papers.cfm?abstract_id=9011).