If you can go to Great Falls in the next couple of days, it's worth the trip. Call ahead to make sure trails are open: the water level is likely to rise before it falls. On Wednesday, the MD boardwalk to the falls was closed (towpath was open) but the VA side was all open -- and amazing.
The DC area definitely dodged the worst of this storm -- there's a post on the VA side of Great Falls showing how much higher the water has gotten in the past. This is really nothing in comparison. And yet it's still a dizzying amount of water. Huge logs are floating downstream. The familiar landscape of rocks is almost completely covered. And it's all moving so FAST.
We also stopped by Carderock to check out the Billy Goat C trail -- which is completely underwater in many places: