I will share some feedback, sorry for the poor english. I had a R500 and now a T540p.
The general reliability is a bit better on the 540, but to be fair, the old R500 had a dedicated GPU that caused higher temperatures and fan activity.
The 540 battery is way better, but it is the normal technology evolution. I assume that all brands and ranges have benefited from this improvement. Same for the weight.
The input devices of the 540 was a terrible regression. No physical buttons for the trackpoint, no leds for capslock and num keys. The keyboard is weaker than the old R500 one. The old one can forgive you for some occasional brutality while typing, when I do that on the 540 the key is simply broken. I miss the old keyboard, sincerely.
Also the screen cover does'nt fit the body when closed. There is a large space and I have to remove dust on the keyboard more frequently.
The T540p still features a magnesium frame and the CPU is hard to overheat but the input devices side is like a shipwreck. Some of these shortcomings was fixed on the following models and I can't wait to have the funds for a P1 or even a T495. I don't think the ergonomcs weaknesses of the T540p was a mistake, all these change saved money for Lenovo.