I agree, if using a shotgun, or even a bow, I like the decoys no more than 20 yards from where I am sitting. It's far enough that your pattern is starting to open up a little more, but not so far that if a bird hangs up coming in, he may still be in range for a shot.

This link to my site might help you some additional info: http://tacticalturkeyhunter.com/?p=337.

Good luck this spring.