How about a site that is a public issue tracker for all sites (or at least ones that dont have their own). So this user could go to this service and issue a bug report for news.ycombinator.com. Other users could look at the bug and say "hey I am having this issue too". Repeatable bugs get floated to the top etc...
Of course, its only good if someone looks at it and responds. But, if this site had enough users, the community would be able to comment and help, and eventually, any service provider that cares about their users might want to be involved (and they can 'claim' their domain somehow).
I think the key point is that you would not expect a response 100% of the time, so the service provider does not need to take time to respond to all issues, only those were several people experience it.
This probably exists though?