ytswy - 9:56 am on Feb 27, 2008 (gmt 0)

Configuration > Maximum Values > Search Results

This controls the number of items before a split in customers.php and orders.php the admin section.

However it also controls the number of products displayed before a split in a category listing (and presumably a search result listing) that the customer sees on the main site.

I don't know any way of using different values for these without editing the php yourself - although I'd be surprised if there wasn't a contribution somewhere to do this.