APP_PAGE_ID

A while ago I promised tips & tricks .... well, for starters:

Supporting the end users of an Apex application is much easier, when they can tell you the relevant page number. Of course it is in the URL (as long as the Apex URL is not hidden, e.g. with a frame redirect), but in my experience end users like a more explicit way of getting the information.

For this reason, I include &APP_PAGE_ID. in the Navigation Bar of my application.