Don Norman, The truth about Google's so-called "simplicity":
If you want to do one of the many other things Google is able to do, oops, first you have to figure out how to find it, then you have to figure out which of the many offerings to use, then you have to figure out how to use it. And because all those other things are not on the home page but, instead, are hidden away in various mysterious places, extra clicks and operations are required for even simple tasks -- if you can remember how to get to them. Why are Yahoo! and MSN such complex-looking places? Because their systems are easier to use. Not because they are complex, but because they simplify the life of their users by letting them see their choices on the home page: news, alternative searches, other items of interest.
...which would all be well-and-good, if we (as users) weren't able to remember where to find services we cared about once we'd found them the first time, if we weren't brilliant at remembering paths and landmarks, if we weren't actually first-time users only once, and after that experienced users who are able to discover and learn. The great thing about not putting everything on the front page is that the surface of possibilities increases in line with the user's growing experience.
Perception is memory. If I see a page full of possibilities, it's like I'm remembering them all at once. A page that hints at possibilities lets me remember only what I care to remember. Google's IA challenges are not how to present everything, but how to make everything discoverable initially, and keeping found things found thereafter. That's why Google's emphasis on clear subdomains is so good: You bookmark, or remember to type, the perspectives on Google's index you wish to take.
You can both discover by browsing, and bookmark shortcuts plus memory to jump back in, and it's the lack of this pair that makes the desktop point and click interface so limiting. Having everything in the GUI kind of space is like having to describe a location with mime. No chance for "aisle 3, halfway along, 2nd shelf." You have to gesture to your computer, "follow me, follow me" and then mutely point "mmmph."
When Gulliver visits the great academy of Lagado, in Chapter V of Part III (A Voyage to Laputa) of Gulliver's Travels [full text], he learns about their many projects:
We next went to the school of languages, where three professors sat in consultation upon improving that of their own country. [...] The other project was, a scheme for entirely abolishing all words whatsoever; and this was urged as a great advantage in point of health, as well as brevity. For it is plain, that every word we speak is, in some degree, a diminution of our lunge by corrosion, and, consequently, contributes to the shortening of our lives. An expedient was therefore offered, "that since words are only names for things, it would be more convenient for all men to carry about them such things as were necessary to express a particular business they are to discourse on." [...] many of the most learned and wise adhere to the new scheme of expressing themselves by things; which has only this inconvenience attending it, that if a man's business be very great, and of various kinds, he must be obliged, in proportion, to carry a greater bundle of things upon his back, unless he can afford one or two strong servants to attend him. I have often beheld two of those sages almost sinking under the weight of their packs, like pedlars among us, who, when they met in the street, would lay down their loads, open their sacks, and hold conversation for an hour together; then put up their implements, help each other to resume their burdens, and take their leave. But for short conversations, a man may carry implements in his pockets, and under his arms, enough to supply him; and in his house, he cannot be at a loss. Therefore the room where company meet who practise this art, is full of all things, ready at hand, requisite to furnish matter for this kind of artificial converse.