Sorry to crash, but they picked a great place for a convention. I used to work in the same office plaza that the Marriott Crystal Gateway is. You are in walking distance from the Fashion Centre at Pentagon City and you can get to the Crystal City Metro Station without even going outside. (Metro is the subway)
If you are flying into National Airport (they might call it Ronald Reagan but it is still National to me), you are less than a 5 minute subway ride to your hotel...
Here is a map to the subway. Hope this helps
Metro Map
Just want y'all to know that you got me homesick!
If you need any DC area info, I will be happy to help
Homesick Jill