All my clients receive a disk with their pictures to print 4x6s (some packages also include the high resolution files, which can be printed as large as you like - I've done up to 3'x4' with no pixelation).
I am also going to start including a web-ready file folder on your disks, which will include the Dragonfly Logo.
Two reasons - first, copyright.
But second, and more importantly, in this age of right click and copy, microstock, and on-line theft, having the logo on your pictures protects you as well. The last thing you want is your breast-fed baby selling formula or your wedding pictures promoting viagra!
(disclaimer, I am sure those companies pay for all their pictures. I'm just sayin' :) )