When ETFs close down, investors are often the hardest hit. Generally, there is a period between when a fund announces its closing and the final halt of trading. During this period, investors can choose to sell their shares or hold on to their investment in order to receive its underlying value at a future date. Selling an ill-fated ETF in the open marketplace can often be a losing proposition. An influx of sellers and absence of buyers often causes the fund to trade at a discount to its underlying value, or NAV. Investors who choose to wait for redemption have to weigh the opportunity cost of having funds tied up. In the case of UMM and DMM, investors will have to pay up as the funds wind down. MacroShares estimates that the early termination expenses will range from $0.85 to $0.90 per share, or about 4% of the share price. Structure and liquidity are important factors in determining the viability of an ETF. While a fund may track an important investment concept, sometimes it fails to attract investors or has a strategy that fails in open-market trading. UUM and DMM may have been the only ETFs to track the Case-Shiller indexes, but investors have other options for betting on real estate in the ETF universe. REIT ETFs, such as the SPDR Dow Jones REIT ETF ( RWR) and the First Trust S&P REIT ( FRI), provide different ways to access the REIT marketplace. -- Written by Don Dion in Williamstown, Mass.