Ive been using Drago for a few weeks now and think it is easily the best SGF editor (for windows at least) that I've come across.
One suggestion I have, after using it for a while to annotate games including out alternative move sequences is that if you place letter markers on the board 'A', 'B', 'C', etc. and then have move sequences that start with those points, would it be possible to mark the stone in the move tree with the letter? this would make it really easy to see which sequences in the tree started with which moves on the board.
ive uploaded a mocked up screenshot to explain what I mean:
http://users.on.net/~flippy/Drago-suggestion.jpg
cheers
ben