(Image Caption: Services in Snow Leopard are now in the contextual menu, and contextual in nature.) In 10.6, you'll be able to individually disable or enable each service, which is a great improvement in its own right. However, you'll also be able to get to services from more places--they'll be available via the contextual menu. What makes this change even better is that the services items themselves are now contextual too. That is, you'll only see the services the are compatible with the selection you've made.
In prior versions of OS X, non-usable services were grayed out, leaving the menu cluttered and ugly looking. In 10.6, the non-applicable services simply won't show at all. Finally, Automator will let you build your own services, making it easy to turn a repetitive task into a simple mouse-click exercise. I think this may be one of the more exciting areas of change in 10.6, for it really turns the Services menu into something that literally any user can take advantage of.
Two other improvements caught my attention as small changes that many users will welcome. The first is related to selecting text in Preview. If you've ever tried text selection on a multi-column document, you know it's not fun--typically, you wind up selecting text across columns, instead of just down your desired column. In Snow Leopard, artificial intelligence is applied as you make your selection, helping Preview select just that text you're interested in copying. I would love it if this technology could make its way across app that supports multi-column documents!
The second small change is to an area many users may not think twice about, but if you work with a lot of removable media, you'll welcome this one. You know that annoying message that lets you know you can't eject a disk because it's in use? It's annoying because it doesn't tell you anything about which file may be keeping the disk busy, just that it's busy. In Snow Leopard, Apple has made changes so that fewer events will cause the disk to report itself as busy. Beyond that, though, if the disk actually is busy, you'll see a message that--hallelujah!--tells you exactly what it is that's keeping the disk busy.
One final new feature is actually a really old feature. Snow Leopard will have a Put Back command that moves a file from the trash back to its originating folder. The long-time Mac users out there will remember this command from OS 9 as Put Away (Command-Y; it's still in my memory banks), and it's very useful for those times when you change your mind about deleting a file. Score one more for the old timers!