Well I am the proud owner of a PF50 and I think it's a marvellous product, for the price I paid. I'll be honest, I wouldn't pay £300 for it - but then again, living in England, I probably don't have quite such bad mains issues as you probably had, which would impact my thinking.
Anyway - to the product. It is built like a tank and very well constructed. Its mains cable accounts for over half of the weight of the product, from what I can make out and is as thick as my thumb, its a little inflexible, but thats not a quibble. There's lots of flexibility in set up, which I haven't had the time to fiddle with yet.
As for the impact on my system. I've found that it has removed any audible clicks and pops from my sound - I used to get a lot from the fridge/freezers, the central heating, the kettle! It does seem to have improved the picture on my Kuro somewhat. I thought I was imagining it, but Mrs S thinks the same, and the picture does seem clearer and more stable. Now as all my sources (DVD / BDP / Cable box) and the TV (both screen and media box) are all plumbed through the PF50, I'm not sure whether it's source stability (my AC voltage seems to vary from 236-244V) or the display's happier with the smoother supply, I can't tell. But it doesn't matter - it's better, and that's all that's important. Sound does sound good - haven't noticed the "closing in" of sound that some people say they've noticed with the PF30 and PF40.
Overall a big thumbs up
P.S. If I get a chance I'll post what's plumbed into what socket and post that proper review of the PF50 I promised a month ago