Keep in mind most of the data going to these sites is coming from different sources, as well as being updated at different times. I would take most listings you find from secondary sites with a grain of salt. For the most accurate source of market activity you may want to use http://www.MlsListings.com. Our local Realtor boards have standards on keeping the data up to date, but as the data is moved and manipulated it becomes less accurate, and as with any type of data points, it is only as accurate as its source.
Also, the Foreclosure data may not be accurate for a few reasons, first it may be encompassing short sales, notice of defaults and foreclosures in one place. These are different stages of the foreclosure process, and should never be melded together. Moreover, the banks are not in the business of sharing data, and many are not even filing NOD's even though the house is up for shortsale or already being sold by the bank as an REO.
Good Luck House Hunting!
Eric & Janelle Boyenga
Top 1% Intero Real Estate
Silicon Valley Specialists
"Guaranteed Results through Teamwork"
Yahoo's numbers seem a little high. According to our local Multiple Listing Service (MLS) there are only 10 (6 sale pending) single family homes and another 23 (15 sale pending) condo/townhome's REO/Short sale/Foreclosure properties in Mountain View. Yahoo may include houses that have had a notice of default filed, but the property hasn't been officially listed for sale.
There may be other foreclosures that are not listed as such, but you're probably fairly close.
Yahoo Real Estate, like most other real estate sites, simply pull their data from the Multiple Listing Service.
If you're thinking of buying a foreclosure property, I'd suggest getting some professional advice. I have clients looking at properties that seem reasonable, foreclosure and standard. There's one that seemed OK and we've just found out that there are 22 other offers on it. This is very, very common. The properties are listed way cheap simply to attract a feeding frenzy.