An additional point about DOM.
DOM means "Days on Market"--how many days that house has been listed. It can also refer to average days on market--for instance, perhaps that average days on market for homes in Fairfax is 56 days. For accurate statistics, see http://nvar.com/monthly-sales-market-data-reports/august-2011
DOM for individual properties can be misleading. There's also DOMP--days on market for the property. A property might be put on the market, not sell in 180 days, be taken off the market, then put back on. A quick look might suggest that the property's only been on the market for 10 days. But DOMP would show not just the current 10, but also that previous 180.
A house with a significantly higher DOM than comparables can indicate that the house might be overpriced or doesn't show well.
Hope that helps.