I've demoed one with SD Sky channels over Scart. It's a mixed bag. The higher bit-rate channels (BBC, Sky 1 etc) really do look excellent - I can only imagine how good the HD versions would be. However, such a large screen can't do wonders for the lower bit-rates used by many of the channels so it does serve to show those up more than a smaller screen would.
Still, having said that, it's the best tv I've ever seen and I was, for a few crazy moments, considering selling a kidney. Seeing the I Robot blu-ray demo disc running on it alongside a bunch of other tvs running the same feed, it was clear how superior it was. If you've got the money to spend and are looking to buy soon, I wouldn't hesitate. My one bit of advice would be to budget for how to get the best out of it. Definitely look for a decent stand-alone Blu-Ray deck like the BDP-51FD to go alongside it. If that stretches the budget a bit, look to the LX5090 instead as there's not a big difference between the two.