If you want a taste of some of the functionality of Time Machine, the back up system in Leopard, check out TimeDrawer from our friend at OneRiver Software, Masatoshi Nishikata. OneRiver developed the interesting Edgies app I reported some time ago. Edgies allows you lots of drawers and pull out postits on your desktop.
TimeDrawer logs changes you make to documents, and their history over time. You select the type of document you want to keep track of, then TimeDrawer will save different versions of them for future comparisons. You can watch TimeDrawer do its stuff as you save documents. And you can access the history of a document by selecting it and accessing the contextual menu (right mouse click, or the cog in finder windows) and selecting TimeDrawer.
As far as I can see, TimeDrawer works best with text documents, allowing you to compare content of different version. And it looks something like the Time Machine previews show. I installed beta 6, and recently version 1.0 of TimeDrawer a couple of days ago. So, I don't have much in the way of long term document evolution to track yet. However, the app seems to be fast, unobtrusive, and seems not to be a resource hog. Hopefully, I'll feel the same way in a week or two of testing.
Give it a try, and post your opinion here if you like. And, BTW, I found this via MacDevCenter.