If a stack contains many items, it appears in this grid view. Files downloaded in Safari or Mail automatically appear in a downloads stack.
Cover Flow Is in Finder
Leopard's reworked Finder now permits you to flip though your documents and images using the same Cover Flow interface that iTunes employs to let you browse thorugh album covers. You can flip through multipage documents or play videos right in Cover Flow.
Preview Icons
Even the normal icon view for files should look a bit more detailed. The same attractive thumbnails that drive Cover Flow appear here as well.
Quick Look
View files without opening them, using Quick Look. Apple promises that this file viewer will work with nearly any format on your system, including videos and multipage documents.
Reflective Dock
It may not be the most useful feature, but the reflective dock in Leopard sure looks nice. Drag an application window down toward the bottom of your screen, and you'll see its reflection in the dock background.
Spaces
Virtual-desktop fans will want to check out Spaces, which lets you build multiple desktops for different projects or activities.
iChat Backdrops
New backdrops and photo effects let you spice up your iChats. Add in the appropriate backdrop, and you can make it look like you're chatting from Paris.
iChat Theater
Collaborate with other users or just have fun sharing files in iChat Theater. You can share any file that works with Quick Look while chatting.
Front Row
Leopard's updated Front Row interface looks much more like Apple TV.
Mail Notes
The latest update to Mail supports handy little notes that get synced to your mail server, so your reminders can follow you everywhere.
Mail RSS
Apple has also built in the obligatory RSS reader, but searching and Smart Mailboxes make finding things within your feeds easier.
Stationery
Support for stationery lets you jazz up your e-mail with HTML-based templates.
Time Machine
We've known about Time Machine, the automatic backup feature built into Leopard, for a while now. Connect an external drive, and Time Machine will offer to begin automatically backing up your files.
Time Machine (Part 2)
If something goes wrong and you'd like to retrieve a previous version of a file, simply fire up Time Machine and use its timeline interface to zip back to the last time you edited the file.