I
use GEDitCOM II v1.7 a lot -- for my own trees and for friends' data,
and I have not lost data for a long time (and even then, it was just the
trailing piece of a buffered string, before that issue was fixed). Are
all your other programs working fine? If you open the Console utility
application, do you see any alarming messages? Is there anything
unusual about your configuration, like a netwokred drive?
I am using OS X 10.6.8. What version are you using?