There's a whole lotta data up in D&S's recent article on apartment ROI. The article suggests most apartment investors, even in the worst of times, still made money (4% CAGR) though that's probably because they hold property for a >10 years. Yep, these are serious Investors, not flippers a few years out of college.
According to D&S, the folks who bought an apartment in 2007-8 will likely be underwater for 4-6 years so if you're an investor, be happy renting your apartment out for several years before you can realize significant appreciation or try and sell next year and redeploy the capital elsewhere.
In short, buyers these days should look at real estate as a long term investment, especially those who bought at the top of the market.
See the full article here.