This article is overall, probably not a big surprise:

http://biz.yahoo.com/ap/080306/home_equity.html

But here's a startling fact:
Moody's Economy.com estimates that 8.8 million homeowners, or about
10.3 percent of homes, will have zero or negative equity by the end of
the month. Even more disturbing, about 13.8 million households, or
15.9 percent, will be "upside down" if prices fall 20 percent from
their peak.

Scary.