What is the maximum number of pages that can be saddle-stitched?

The maximum number of pages depends upon the weight of the paper the booklet is printed on. This is because the staples (or stitches) can accommodate up to a certain thickness. Also, the sheets are folded after they are stitched, so if the spine area is too thick it will not fold nicely and can "bubble" open.

Generally, booklets of 40 pages or less printed on up to 100lb text will lay flat or having minimal bubbling. If the paper used is in the 50-70lb text range, the page count can be up to 64 pages with little or no issues.