The Pioneer is an ok up-scaler but don't expect miracles on a 50" screen. Watchable is about the best compliment I can make though its as good as most others. Excells with BR and SKY HD 1080i material though. Philips new RGB/LED LCD's are also phenomenal imo but expensive for 42". Better upscaled SD pictures than the Kuro but thats probably also partly due to the smaller size.
If you have a tighter budget and watch a lot of non-HD stuff I'd personally save my dosh and go for a good HD-ready set that accepts 1080p/24f signals or you could consider Toshiba's newly launched series of LCD's which use their proprietary upscaling circuitry, similar to the one used in their excellent XDE-500 DVD upscaler which I have. To say it makes a difference is an understatement and if it is anything as good, those sets should make SD viewing a pleasure compared to the competition. These sets go up to 46" I believe and are full HD/1090p panels. Some tests elsewhere praised them highly.
I've mentioned this a few times though as usual on this forum, people are
rarely interested in brands other than the usual suspects.