Hello from Germany!
I like the printed year book but an online only would be OK for me. I
think the data would be fairly safe if we have a password protected
members-only section on our website.
But there should be a printed version on request for people who don't
use the Internet.
Another thing possible would be to put the data from the first pages
(by-laws, lists of charter members etc.) online with a printed
version for new members, and have only the membership directory
printed in a smaller booklet.
Or instead of having an online version on the website, the yearbook
could be sent as a pdf-file to all members once a year.