Personally I think it's a good thing to do to plastics. The only downside is you have to be a little more careful with it.
On carved decoys I think it takes away from the bird. The carver has an intended "look" he is conveying in his work. Covering it with anything other than paint takes away from that and hides a lot of small imperfections that make it a handcarved bird...in my personal opinion. I personally love seeing small cork voids in a bird and some wood grain. It only builds more character over time and looks better...not worse. We never repaint or repair cork and wood birds....they look "beautifully used" after 15 years or so and the birds couldn't care less. Again....it's all personal preference for me.
With regards to foamers it has a great fit. It's a fantastic way to hide seams, burlap, etc. Those type birds generally have no detail carved in them due to the medium so it does wonders for the way they look.
I personally like the way the black flocking looks on a bird...but I would never hunt with a flocked bird because it is not durable enough for the way I hunt. I'm not saying it doesn't work great for a lot of other guys but it does not fit our operation...and has proven itself not to.
It has it's pros and cons and depending on who you are talking to you will only hear one side of the story. I say try it and see if you like it. If it fits your hunting style roll with...if not then leave it behind. Nothing is perfect and nothing kills birds everytime. There's no such thing as a "silver bullet" in duck hunting. Rely on YOURSELF....not your decoys. Then you'll never have a problem killing birds
That's my $0.02 on flocking.
"Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius -- and a lot of courage -- to move in the opposite direction."