Ive only used an inline amp on one site, starchoice install at a casino, they required 800ft of cable and wouldnt pay for the RG11. I put the amp at around 200ft mark and Ive got adaquate signal quality at the end of the run.
think of it like this, youve got poor signal, like am radio, sounds crappy right ? now walk 800ft away, sounds like crap quiet radio now right ? now crank the volume on the radio, not its louder, but sounds still pretty crappy right ?
now take a nice dvd audio disc, sounds great, now walk 800ft, still clear, but way to quiet. crank the volume, defn doesnt sound as good as upclose, but at least you can hear it.
an inline amp doesnt improve the quality, if anything it hinders it, it just makes it louder, sometimes this is required, but honestly only over very long distances. you only use an amp when you HAVE to use an amp.