nonmonotonic

I had. It is due to the way OS X calculates the setting of ntp.drift. I never actually tried this because it happens rarely to me so experiment and see what happens. Here's more stuff pertaining to this problem ( for what its worth ). Enjoy PS I believe problem will also go away if the Macs are powered off each night as ntp.drift is recalculated on start up.

I maybe wrong but I believe it IS a proxy server problem. In my college we use a Windows proxy server which worked seamlessly with our windows machines. The Macs however were regularly asked to authenticate. So now we use a Unix box for the Macs without issues. seems to point to iPhoto not being the problem.

Have you looked at redirecting cache files? If you do not have have a fast network, the applications you mention will clog it up with cache traffic. By default the cache files will be stored in the network home folder (not sure if that is true with AdmitMac).