Leopard only: A lesser-hyped feature in Mac 10.5 is Web Clips—the ability to turn a section of any web page into a Dashboard widget. We're not huge fans of gadgets and widgets around here, but Dashboard Web Clips can be a big timesaver, because it lets you check several pages you might otherwise manually refresh throughout the day in one keystroke, no browser required.
Adam got me using Dashboard Web Clips to keep tabs on various Lifehacker stats and graphs; you can also easily track eBay auctions, online fantasy sports rankings, or social sites like Twitter or Facebook in one shot with Web Clips.
If you haven't tried out Web Clips, here's what you do: using Safari, browse to the web page you want to clip a section of. From the File menu, choose "Open in Dashboard." Resize the selection tool to fit around the area on the page you want to add to your Dashboard, and click the Add button. Wash, rinse, and repeat for as many page areas as you'd like (and can fit on your Desktop).
Now, when you invoke Dashboard (by default, the F12 button), your clips will automatically refresh and display their latest state, no browser or tabs required. Sometimes Dashboard Web Clips can get resized incorrectly (if say, you haven't logged into the service you clipped), but for the most part it works quite well.
Have you clipped any web pages into a Dashboard widget? What do you use Web Clips for the most? Let us know in the comments.