I really haven't skated much at the Archives, even though it's just a little ways down the street from the library. From the pictures you can see that it's got lots of smooth marble, and some fun steps. I don't really know what the bust factor is, so watch yourself skating here.
Long smooth granite ledges are what DC skating's about.
The Archives is kind of the end of the circuit going from Pulaski, to the Library, to here, which makes for a great day of skating, even if you do get kicked out of the spots quickly.