I once read a post by a person who had over 50,000 Pages on his site. That is a special case obviously, but consider our lookup system. We’re going through these rules one at a time. With our first method, our rule list was only 10 rules, maximum. With this new method, you add a rule for every single Page you make. Going through 50,000 rules takes a lot longer than going through 10. And even just building that list of rules can take a long time.
Basically you’ve created a performance issue. Your Pages now won’t scale to unlimited numbers. Your site’s speed is linearly dependent on the number of Pages you have.
This is a bad thing.
Much of this is fixed in 3.3, however 50k pages is still going to slow things down a bit 🙂