Very happy logTen user, although i've not felt the need to synch it with my iphone.
As regards transferring data from existing paper log book... All i did was "invent" flights that brought forward the appropriate totals from the previous log book - for example i've got one flight with xxx hours of S76, another with yyy hours of B206 etc. In the Comments column i annotated it as "Carried forward from previous log" and no-one has ever questioned it. I found it comparatively easy as long as you make sure that you list all the correct permutations of Day / night / P1 / P2 etc. It imports all the existing hours and as long as you keep the original log books then you still have the actual record of those flights.
Would have been easier if i'd had the electronic log from the start, but at the same time, i quite like that fact that all my training and my first few years of flying are recorded in a tangible form - for sentimental reasons if nothing else.
Cheers
Barny