Vista is turning out to be Microsoft's Copland (rather than its System 8). The thing is that Apple was smart enough not to ship Copland.
Copland was Apple's much vaunted successor to Mac OS that had all this revolutionary stuff under the hood but which didn't actually (a) work or (b) run legacy software. After many delays it was axed.
After Jobs returned to Apple, System 7.6 was gussied up in Copland's default theme and shipped as System 8 (which is what Copland would have been called if it had shipped). Anyone who had been following Apple knew System 8 was little more than System 7.6 with prettier graphics, but on the plus side it worked very well and was extremely compatible with older software.
After Longhorn's many delays and feature purges, it seemed that anything revolutionary about Vista had been scrapped and that what we were in fact getting was Microsoft's "System 8", i.e. their last gen OS dressed up in their cancelled next gen OS's graphics. This seemed like a rational choice: everyone likes XP, and no-one has any choice of OS when they buy a PC anyway, so sell them XP disguised as Vista and cry all the way to the bank.
Unfortunately, Vista seems to have all the vices of a revolutionary OS (it breaks almost everything) and very few of the virtues (it offers almost nothing new*). With the revelation that if you want Photoshop for Vista you'll need to upgrade to CS3 Adobe has basically verified that Vista is less able to run legacy software than Mac OS X was. Another milestone!
So far, the only third-party application I've run under Vista flawlessly is Notepad++ (an open source programmer's text editor) and pure web application (but bear in mind, I've had trouble with every browser, including IE, under Vista). Everything else from games to office software has issues.
Mac OS X -- which was truly revolutionary -- ran 32-bit clean pre system 7 apps flawlessly. (Actually, Apple's switch to Intel was more painful... but nothing compared to Vista.)