I Found some pdfs earlyer today about xcode and iOS, but that was for 3 and 3.2 All of them were free.
I believe i have seen a referance ón Apple.com but i have searched for xcode 4.1 and it did'nt come up with anything. But i Found a 4.0 userguide at
developer.apple.com/library/ios/ipad
Books.com have Got a couple of xcode4 books some are only available As a nook-ebook - "iPad iOS 4 Development Essentials - Xcode 4 Edition
by Neil Smyth" and then there was one by a Richard wentk called xcode4. Only a few months old.
I downloaded some podcasts today about iOS programming by a rose hulman. Most of Them are between 30min and an hour long. Most of the 38 casts.... ....
I liked watching those videos from last year's developer's conference. I think they are free for anyone with an iOS license. Really helpful, and they introduced a number of differences between 4.0 and earlier versions of xcode