Hi Dave,
I took delivery of the Samsung LE40B650 yesterday and can say that is total rubbish!! It even has a 'Game Mode' to provide quicker respose times although depending on the game that can lead to a very slight lessening of picture quality but i have not experienced this ATALL. I own a PS3 and Xbox 360 and can assure you that i tested it thoroughly last night, i played COD4 and WOW online with no input lag atall in fact it was a considerable impovement on my sony 32". I played both consoles and have had absolutely no probs, be it offline of online.
The Samsung TV is a corker by the way and i couldn't recommend it more and i too was wondering what TV to purchase at that size/price point and i looked at EVERY set in my budget. As a good tip i found the best price online was at Amazon £743 incl next day delivery!! You have to take up the free trial of Amazon Prime to get the next day delivery but it's free as long as you cancel it within 4weeks, you can't say fairer than that!
Hope that helps but if you have any more questions i would be happy to answer them...i have the TV infront of me after all!