N.Y. Times: "At the end of 2006, 24,200 units were on the market in the Washington area, up from 13,000 at the start of 2005. Sales have slowed to 663 in the fourth quarter of 2006 from 3,520 in the first quarter of 2005, according to Delta Associates." OTOH, sales of single family homes seem to be picking up a bit, at least in the inner suburbs. Because condos, townhouses, and single-family homes are at least to some degrees substitutes, such a disconnect won't last long.
Nine(!)-year supply of Condos on D.C. Market: