Time Machine status
By default, after installing the update, Leopard sticks a Time Machine backup status button in the menu bar. This drop-down menu will give you the time of the last backup and a "Back Up Now" option. You can also enter the Time Machine interface right from the menu bar, meaning that you can now remove that semi-pesky icon from your dock.
People were unhappy to learn that Leopard would only have a Translucent Menu Bar; meaning that you would be able to see your desktop through it. Well, Apple has made things better in the 10.5.2 update -- you can now turn this off. Just visit the "Desktop and Screen Saver" System Preference pane and un-check the "Translucent Menu Bar" check-box in the "Desktop" tab.
With "Translucent Menu Bar" off
One of the touted features of Leopard, stacks, also received an update. You can now see your stacks with a "list" or hierarchical view (just like folders looked like in Tiger). All you have to do is right-click on a stack in your dock and select "List" from the "View content as" options. When this is turned on, you can left-click on your stack to see a menu appear with the folders contents (just as it did in Tiger). You can even take this a bit further and select "Folder" from the "Display as" options to get rid of the file icons and show just a standard folder.