I seem to remember being able to get TortoiseSVN to set the last-modified timestamp for files to the timestamp from the revision when performing an update. So if someone committ
I am not sure if Tortoise uses the SVN client as a backend, but if it does, there is an option in the Subversion configuration file:
use-commit-times = yes
Sorry if this doesn't apply on your platform, but I'll mention it anyway. It works for those using the SVN command-line client.