Unfortunately, none of us have a crystal ball. We can all speculate, but who knows who's going to be correct. It could easily be a few years before they start going up again. In the mean time, the values may (or may not) continue to go down. With foreclosures on the rise, the latter may very well be the case. But then again, the Washington, DC metro area has an incredibly strong economy, which helps local real estate values tremendously.
Some things to consider:
If you are buying a home to live in long(er) term such as 5+ years, then you're buying a "home", not a short-term investment and you should be alright. Property values always go up eventually and it's one of the safest long-term investments you can make.
If you're going to live there for less than 5 years, then you're treating real estate as a short-term investment and you may or may not want to buy something now.
For my opinion, check out this blog post, which I just wrote today - http://realdiablog.typepad.com/weblog/2008/01/the-bottom-of-t.html