I would like to be notified when a question is posted with a particular tag. I can't see any way of configuring this within the PPCG site. I am sure the SE people would not like lots of bots constantly reading listings by tag, looking for changes. Am I missing something? Is there a way to turn on such a notification?
Yes, there are two ways to do this:
If you are following a single tag, probably the easiest thing to do is to go to the tag page (e.g., https://codegolf.stackexchange.com/questions/tagged/code-golf), then go to the bottom of the page and save the feed link. You can use this feed with any feed software of your choice.
If you are following multiple tags, or if you prefer to get email notifications, you can use the Stack Exchange filters feature at http://stackexchange.com/filters. This allows you to set up filters for multiple tags, or specific sites, or whatever you want. Then you can either set up an email subscription (at most one message every 15 minutes), or you can use the feed link with your favorite feed software.