You are probably right to be concerned. Unlike some other embedded Linux distributions, Zeroshell insists on logging a number of items to a disk based file system.
After about 1.5 to 2 years of use I started having problems with my net5501 Zeroshell box that I attributed to the compact flash card wearing out. The net5501 Zeroshell setup uses the CF as its disk.
Wasn’t too hard to fix: Make sure I had a current profile saved to my laptop, flash a current version of Zeroshell to a new CF, install the new CF and up load the saved profile back to the box.
I’ve considered temporarily removing the CF and making a copy of it with dd so that I can quickly setup a new CF and throw it in if required. But I’d probably have to still upload a current profile as I have a tendency to make changes every couple of months.
So if you are running in a commercial environment, I’d really recommend you run on a server class machine with a profile/logging drive that can handle the writes. For home or SOHO environment, it is a bit less than ideal but if you are willing to throw a new flash drive at the box every year or so you can make it work.