I get frustrated when the transfer to digital is bad, as when older books are scanned in without being proofed (by supposedly respectable publishers, I mean, not freebies), or when even recent books contain errors (missing accented letters, for example).
The convenience is a massive bonus. Since I d/l things basically at the point of reading them it is also economical (no hunting, hoarding, storing involved). Plus if you want physical copy instead no-one is stopping you.