I was able to get good deals during the 90's, then did not buy anything from 2001-2008 because houses were overvalued so much that nothing in decent neighborhoods would cashflow. (I sold many of my properties in 2007-2008) I have been purchasing again from 2011-2016, but it is getting close to the point where I will not be buying anything again. The trick is to look at cashflow in decent neighborhoods. If you cannot find that, then it is a bubble in my opinion. It is hard not to buy when other people are getting big appreciation, but it is also hard to declare bankruptcy when the bubble pops. I prefer to minimize risk. I sleep well at night.
(Since I live in the Midwest, it is easy to find cashflowing properties and the courts are landlord-friendly. I am not sure I would want to buy real estate in areas that do not cashflow well, and have tenant friendly courts.)