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
When I go to the Settings option in the TortoiseSVN menu, I see an option to "Set file dates to the last commit time." This may be what you're looking for.
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.