we bought a Mountain View duplex in 1991 near Sylvan Park, at the top of the market, we paid 500K and then it promptly was underwater for a few years, but now is worth double what we paid. and it has worked out great as we have my dad living in other half. HOWEVER If we had bought a single family in Los Altos for 500K in 1991, it would likely be worth 1.5 today. maybe more depending on improvements and location. In this crazy market I would not buy anything assuming appreciation over next few years, but overall duplexes are great investment properties if the cash flow works for you. Sunnyvale Duplexes are a better buy.