No one is unhappy with Mac OS X Version 10.4, known as Tiger. OS X is not an application platform (I bristle at using the term "operating system" for OS X; I explain why below) that needed repair, speeding up, or exterior renovation. Motivations for major upgrades of competing system software -- roll-ups of an unmanageable number of fixes, because the calendar says it's time, or because users are perceived to have version fatigue -- don't apply to OS X. Apple wields no whip to force upgrades because Tiger stands no risk of being neglected by Apple or third-party developers as long as Leopard lives. Despite the absence of a stick that drives users into upgrades of competing OSes, or perhaps because of it, Apple enjoys an extraordinary rate of voluntary OS X upgrades among desktop and notebook users. Why? People buy Macs because the platform as a whole is perfect, full stop. Leopard is a rung above perfection. It's taken as rote that the Mac blows away PC users' expectations. Leopard blows away Mac users' expectations, and that's saying a great deal.
Apple's secret, which is no secret to Mac users, is that major OS X releases deliver tangible value far in excess of their asking price, which in Leopard's case is US$129. OS X is, first and foremost, a platform for integrated, user-facing applications, and to a far greater extent than previous releases, OS X Leopard itself exploits the facilities that Apple's developers have used to create the vendor's commercial software. Apple hasn't reserved any of the Mac platform's goodies for itself, and users don't need to wait (or spend) for apps that expose the platform's richness in productive ways. For example, Screen Sharing is now built into OS X; just open the Finder icon for a remote server and click the Screen Sharing button to grab the remote system's display, and optionally its mouse and keyboard. Apple built Screen Sharing into iChat, and Back to My Mac uses the .Mac service and Screen Sharing to securely tunnel to files and consoles on Macs behind firewalls. All of Leopard is like that -- every Leopard feature, even those that would ordinarily be invisible to all but developers, or reserved for the use of the vendor, is planted throughout OS X in the places you'd put it.
Freedom in the frameworks
Looking at it from a technical perspective, Leopard's step past perfection lies in its extensive use of the combination of the Mac platform's intrinsic integration and Leopard's delivery of hundreds of additions and enhancements to OS X's frameworks.
Apple supplies a consistent, familiar, and well-documented path for developers to do any given thing. In contrast, an entire industry has sprung up around providing developers with proprietary plugs for the gaps that Microsoft leaves in Windows, often intentionally as an aid to the third-party development community. The completeness of the Mac frameworks leaves no room for a marketplace for Mac developer library enhancements.
What's changed in Leopard is that Apple has invested enormous effort to expose Mac framework enhancements to users through OS X's built-in facilities and applications. Leopard's out-of-the-box experience, which I define as the things that a user can do without spending an extra dollar on software, eclipses Tiger's, and Tiger was no slouch in this regard. In the past, third parties have offered freeware and shareware facilities to extend or even replace Finder, the Mac's answer to Windows' primitive Explorer. That died out with Tiger, and Leopard makes such efforts entirely useless. That is not a bad thing.
Unlike Microsoft, Apple is not afraid to put developers out of a given line of business. Leopard integrates e-mail, browser, calendar, search, preview, dictionary, thesaurus, media player, code-free scripted workflow, accessibility, and almost innumerable top-level bundled apps and capabilities that, in one sense, take out any market for supplanting these things. No matter how well Apple does something, someone has cooked up what they feel is a better, but usually just different, way to do it. Leopard addresses that. Rather than seeing Leopard as a popping of the balloon for third-party enhancements to the Mac's core user experience, a more accurate way of looking at it is that Apple frees developers from trying to improve on that experience. Third parties can focus on new applications instead. Yet, Apple's 300-plus features are all things that third-party developers have at their disposal without requiring any hacks or workarounds to get at. If this registers somewhere between confusing and unbelievable on your scale, I understand. Apple has always let users and developers make their Macs into anything they like. Leopard moves the line between top-level functionality that can be improved upon and baked-in user-facing capabilities that don't need improvement.