It's been about a month since CBS MoneyWatch last looked at real estate investment trusts (REITs), but the continued interest of investing in real estate makes this an asset class worth looking at again, especially since some metrics are indicating that valuations have reached high levels. 

The attraction of REITs lies in their high yields relative to safe bonds, such as U.S. Treasuries. For example, while the 10-year Treasury yield stands at about just 1.7 percent, the yield on the Vanguard REIT Index Fund is almost twice that at 3.3 percent (as of Dec. 15).