When Apple's plans for Snow Leopard first became public knowledge, people worried about the lack of new features, and that Apple would gouge users for 90 quid or so. Now Snow Leopard's here, it's 25 quid and surprisingly feature-rich.
As always, there are some negatives. Apple not installing Rosetta seems like unnecessary needling to get devs to update PowerPC apps, and a similar quirk affects System Preferences, which reloads in 32-bit mode when third-party panes are accessed.
Malware protection is finally bundled and worked fine on a couple of dodgy archives we located, but only time will tell how effective this aspect of Snow Leopard is, and Intego claims Apple's XProtect system doesn't recognise all the variants of the trojans it's supposed to protect against.
Overall, though, this is a point-zero update that feels surprisingly solid, and although many changes are technologies that perhaps won't be fully exploited for some time, we wholeheartedly recommend Leopard users upgrade anyway (as long as the apps you regularly use are fully compatible - check the Wiki to be sure). And that's because you get a faster Mac, a bunch of hard drive space returned to you, Exchange support, quality enhancements to Exposé and the Dock, and myriad touches that make using your Mac a more pleasurable experience.