There actually are a lot of significant upgrades.
Spaces is good for partitioning your desktop if you are working on a lot of different projects at once. Time Machine automatically archives your system and saves it so you can recover deleted files years later.
There are a lot of other smaller bells and whistles. I, personally, am really looking forward to stacks because I hate clutter. It's not a complete new OS, just another variation of OSX, so the additions will be small but I really like some of the things they added.