Great feature!
Everything works just fine; castling, en passant, underpromoting, all the technical stuff is perfect.
The only thing I can think of is that there is no list of moves, so you don't know for sure whose move it is unless you remember the last move or try out to see what it'll let you do. Also, you can't see how you got to the current position.
Those are a couple of suggestions that might help improve it, but it's running perfectly. Everything works great.
You guys have really been doing a good job lately, with Live Chess, Chess TV, and now this thing...
G

can you please help us test this feature?
http://www.chess.com/analysis-board-editor.html
please give us detailed feedback!