You have to understand that a lot of us have seen DC in good and bad times, and our perceptions are often shaped by some of the things we've seen. I've been in and out more or less for nearly 20 years, and I now see houses with granite counter tops and sunken jacuzzis that I remember were once filled with crack addicts and hookers. I was here when a Congressman was mugged on the steps of the Supreme Court, and I now see streets (like Barracks Row) that are so inviting I want to invest (actually kicking myself that I didn't).
But don't take our word on crime--it's always a bit warped by our experiences and views on things.
Go to this website:
Metropolitan Police Department
Input your address and see, statistically, what has gone down in the area over the last few weeks / months, etc. Take a look at someplace like 4500 45th Street, NW, then compare that to say 3000 P Street, NW, or 1600 18th Street NW, then compare that to 600 8th Street, SE, and then compare to say 1400 Good Hope Road SE. You'll see a wide spread across the city, and probably some things in areas you wouldn't expect.
You can then be the judge of what level of edge you are comfortable living around.