It's certain that many won't have the patience to look further than as few as three levels. We certainly can play with these numbers. A broader, shallower hierarchy of 15-entry long menus would accommodate over 750,000 entries at five levels, and over 11,000,000 at six. I'm convinced that Yahoo will eventually lose the battle of breadth vs. depth, but many would argue that this point is moot due to Yahoo's support of searching. Pitch means something different to a roofer than it does to a salesman, a batter, and so on.
Pitch can be a verb, a noun, and is the stem of many other words.
Due to this ambiguity, information searching is just plain hard, regardless of whether you're dealing with Yahoo's index or the card catalog at your local public library. Additionally, searching is only as good as the materials that are being searched. This variability is found in Yahoo's cataloging scheme as well, which currently supports many duplicate and overlapping categories and subcategories. These types of anomalies are likely to increase as the volume of Yahoo's entries increases. To the credit of the folks at Yahoo, professional catalogers are now being hired to work on problems like these.