This field MAY also be used with any 3xx (Redirection) response to indicate the minimum time the user-agent is asked [to] wait before issuing the redirected request.
David Nesting had the thought that this would eliminate the last good reason — other than not having control over your webserver — for using a meta http-equiv=refresh element in HTML. Support for Retry-After in in Mozilla has been requested. It seems also needed in Internet Explorer, Opera, curl, and wget, among others. The test is here.