greekfire, your posting made me curious about Rancho Del Oro, so I looked.
This example below is an illustration what what you were saying about Rancho Del Oro. SDlookup does not show the original sale from the developer in 1990 but it think that it was more. Looks like the original owner sold in 1995 at a loss after holding for 5 years. There’re going to be quite a few such cases in the future.

http://www.ziprealty.com/buy_a_home/logged_in/search/home_detail.jsp?listing_num=071017444&page=1&property_type=SFR&mls=mls_sandiego&cKey=bfv5615f&source=SANDICOR
http://sdlookup.com/PropertyDetails/tabid/53/pid/FC387DC8/Default.aspx

783 MOSAIC, Oceanside, CA 92057**
List Price: $545,000 – $545,000
Sale History
08/24/1995 $158,000
1990 ???

Bedrooms: 4
Full Baths: 2
Partial Baths: 1
Square Feet: 1,957
Lot Size: N/A
Year Built: 1990
Listing Date: 03/02/07
On Market: 4 days
Type: SFR
Status: ACTIVE
MLS #: 071017444