Yahoo posted some suggestions about contacting their postmaster group over on the ymail blog. They also explained what they were doing to solve the problems with response delays.
Some of the problem is being caused by excessive follow-up emails, either because senders did not provide all the necessary information initially or because they are asking why they have not heard anything. Each of these requires more work on the part of Yahoo and throws the queues into further disarray and puts everyone even more behind.
Yahoo asks that people be patient, they are working through things. On their end, they have added more staff to the postmaster team. They also suggest senders can help by providing ALL the information they ask for at http://postmaster.yahoo.com/ before submitting the request. Incomplete requests contribute even more to the backlog as Yahoo employees have to chase down senders to get their full information.