Wikimedia Commons, like many Wikimedia Projects, doesn't generally
block anonymizing (i.e. services/servers that could be used to hide
your identity) proxies unless they are causing problems.
Since commons is less often a target for troublemakers than some other
projects with the same policy, we often seem to have much fewer
proxies blocked. This also important because of the blocking practices
of some governments. Generally our practices do not seem to cause us
too much trouble, but there are some implications.
For one, it means that proxy-blocked users on other projects can get a
'second life' out of their proxies by harassing their target projects
via commons. It also enables various forms of split project
sock-puppetry, and the larger project block logs become handy proxy
directories for troublemakers willing to go after the smaller
projects.
It may eventually become a PR issue with our customer projects, ...
they can't be happy when their troublemakers come back via commons. It
certainly would be if we ever stopped our practice of blocking
troublemaking proxies once they were found.
As a result of these issues, we're slowly blocking proxies over time
... after all, eventually each one will have been a trouble maker at
some point.
This result in another issue: Since we're generally permissive about
the proxies there are a non-trivial number of apparently good
contributors who edit via these proxies. As we block proxies we
continually frustrate and impede these users, who expected commons to
continue working.
I don't know that there is much we can do about this now but I wonder
if other commonslisters had some comments on the matter.