I use mojo decoys a lot. Infact, I have four of them, and often I'll run them all at once. A lot of it depends on exactly how and where I am hunting.

In my experience, when you are hunting way back in the timber and woods, unless you have a big open hole (over 75 yards wide or so), then a Mojo will quite typically do you more harm than good. The reason behind this, I believe, is that wood ducks in particular tend to fly below the tree line and zip through the woods about 20 feet off the water. When they suddenly come upon this white flashing wing decoy, their first reaction is usually, "OH CRAP!" and you'll get a wild flare. There are things you can do to your Mojo that will keep this from happeneing, slight modifications, but I'll save that for another day.

In more open terrain, I've had woodies circle and come right in to them. Singles are usually the best for this.

Honestly, the best way to hunt wood ducks still, in my opinion and experience, is to find an open hole of water where they are landing before swimming up into the woods and creeks, and be set up with a few wood duck decoys right at shooting time, and be carrying at port arms because there usually isn't much of a warning they are coming. Calling usually helps later in the day, or if some are setting a ways off. If you call to them, suprisingly, you can often make them pick up and fly over (using a wood duck call of course). 9 times out of 10 though, when they get up and fly on their own, they will come and check you out if you've been calling to them, and they back to you.