I haven't tried one, but I'm considering it. People say the rear manifold is almost as good as a header, so most of the improvement is to be found in the front. The cost-to-benefit ratio for the plog is compelling. Considering headers are nearly a grand before installation, and their stage two intercooler is $1100, maybe it is better to go with the plog and intercooler? I don't know, but I'm guessing the plog is the better option unless you are going for the absolute maximum amount of horsepower you can get out of a 3800. Which will cost several thousand dollars, and if you need that much performance maybe you should be thinking about LS-swapping another platform.
Plog is only $150 - I think that's the way I'm going.