Equipped with Tim Cooks's public email address, you can do just that and know that somebody — maybe and eventually Tim Cook himself if your message warrants it — will read your email and possibly reply.
Will I Get a Reply from Tim Cook?
Typically, you will not get a reply from Tim Cook himself. It is, of course, not entirely unreported either.
Will My Email to Tim Cook Be Read?
Your email will be read. The first to see it will most likely be a person at Cook's office, however, and not Tim Cook himself.
Important emails may be forwarded to him personally.
(Updated January 2012)