It would be great if Illustrator had a master page like InDesign.
For us who design more then one page for client proofs.
Here is the script. You have to rename it to .jsx and drag-n-drop to Ai window once you have all you numbers selected. If a warning comes up (it gets displayed for external scripts), commit.
Gareth, there is a way to get along without master page using symbols. Create an artboard seized rectangle, group it with some elements, convert into a symbol and paste in place on all artboards. Use a separate layer to lock the all at once. There you have it.
Page numbers is slightly more complicated because it won't update automatically. Create a number on one page. Group it, isolate the group, select all, ungroup (now you have only a type object isolated). Cut it, paste on all artboards. Select all (you are still in isolation and now you have same digits on each page), run the script attached to this comment.
Gareth David commented
It would be nice if there was a basic master page option.
Understand that Illustrator is not a layout program like InDesign, but if your adding features like artboards, to which you can add many, why would you not incorporate a basic master page option to control repeated elements on each page.
And not being able to add page numbers is a pretty basic thing that needs to be added.
This is a great idea