I use a good App on iPad / iPhone - I won't name it as it's still in Beta and not available.
My point is, however, that despite it being backed up both in the cloud and on my own computer, each time I fill a "page" I print it off in high quality, put it in a nice folder and sign the declaration at the bottom of the page to say it's legit. Voila - a paper logbook to satisfy anyone that wants it plus a hard copy backup! (It's my intention in time to have the pages bound properly).
I love the ease of use of the App but I keep a paper copy too.