I know I read in several places that multiple page forms increase the abandonment rate and I think that is the number one reason for the one-click technology that Amazon uses.
The worst approach ever was on a forum I stumbled upon. I read a thread I felt I could contribute to, but I had to subscribe. You know, the we-have-sent-you-a-confirmation-mail thing. After having confirmed - which is an hassle in itself - I discovered that my membership had to be approved! Should I have bookmarked the thread to post afterward? They serious?