Let Down demo is incredible, as well as National Anthem and Motion Picture Soundtrack like Pugeye said. I agree National Anthem is better here. The noisy guitar and feedback and faster tempo is awesome. There's even a totally "new" song "Attention" which is a nice BB-esque pop tune.
Climbing Up The Walls demo is creepy here as well. I also really love that they put that creepy piano part from "Fitter Happier" on here. One thing I really wanted to hear isolated since i first heard it.
I also always preferred the older live versions of "Nude" and this one here is also better than the album version for me. I missed the organ and never cared for Thom's vocal approach on the In Rainbows one.
That bird story with the computer voice really made me laugh.
Overall really great collection for someone who loves OK Computer..