I'm nearly a week into my 28LS35 ownership and the only problem I have is the set's a bit of a whistler (worse in the "smart" full screen mode for some reason). Still trying to work out whether it's me being over-sensitive (my high pitch hearing's still pretty good "unfortunately") or whether it really is outside normal limits.
There are times when I look at the picture (my first exposure to a "big" TV for any length of time) and wonder if it's a bit flickery, but without seeing a 100Hz set side by side I couldn't tell you whether it would be worth paying the extra cash. Certainly I've no complaints about RGB DVD playback... The Blue Planet, for example, is breathtaking.
Anyway, my decision was helped by trying hard to stay close to £500... and the fact I narrowly talked myself out of a Bush 28" from Asda for £250 inc. 3 year guarantee! Not a very inspiring set though
Good luck making your choice.