While you're working on the automation, put a link in the help / about page that points directly to the update page on your website. That will save a lot of hunting.
Be opinionated about frequency and avoid preference configuration hell. Choose weekly if that suits you; most seem to agree that monthly is too long, especially if you're releasing every week. Frankly, I'm not sure I even care what the frequency is. The check box should be "Check for updates," period. Users won't care when the check happens. And for those that do care, include a "Check for updates..." menu item so they can check right away.
In most conceivable real world situations, you probably should just check on every launch. The only reason not to is for load on your server. If your web site can't handle that load, you have bigger problems (the good kind of problem -- you're too popular :-).