just purchased Mac OS X Leopard this weekend, and thus far I am pleased.
I have had no file loss, even my widgets were unaffected by the upgrade.
The best improvements are the Finder, which has a browsing feature not unlike iTunes, and Stacks, which is a handy way to access documents and recent downloads from the Dock. Stacks are also very aesthetically appealing.
I have yet to use Time Machine, as my current external hard drive is a piece of shit.
I've you've got an extra $129, cop Leopard. it's pretty sweet.