I never answer PMs unless it's related to a bug in the game or I know you. And even under those circumstances I still may not respond because I'm either busy, or just don't want to talk.

Others do try to answer your messages as quickly as they are able, provided it isn't spam. Please keep in mind some staff have more on their plate than others, so it may be better to pm a staff that seems less busy, rather than complain that so&so never answers you.