I've got a 2 TB drive in my TiVo HD that currently has about 120 active Season Passes/Wishlists and an additional 50 or so Wishlists that keep track of stuff but don't auto record. Probably about 20 pages of recorded material (and that's with lots of stuff represented only by a folder) and at last check about 140 recorded suggestions in that folder.
Everything works fine, but when I go to re-order anything in the Season Pass Manager, I try to do everything that needs to be done there before exiting as it takes a full five minutes to recompute everything and return to being usable again.