Both my CyBook and TX have better curlability ratings than pbooks.
If I'm lying on my side reading in bed, ereaders are easy to manage - but pbooks mean you have to elevate one portion of the book every other page; if that portion is hundreds of pages it gets awkward to hold out of the way; how did they ever catch on??
I'm currently reading 'Pandora's Star' by Peter F. Hamilton - according to Amazon the pbook is over 1100 pages.
The eversion is much less of a wrestling contest than the pback!