While the WebClips function of Leopard is a handy way to turn various bits of Web content into insta-widgets, there's a more exciting feature in Apple's new operating system that I'm looking forward to: a desktop version of Wikipedia.
It comes in the form of an added resource for the Dictionary app--Apple's in-house solution for word lookup. In Leopard you'll be able to look up a word in Wikipedia without actually visiting the site, or relying on the awesome Wikipedia Dashboard widget. Even better, using the on-the-fly lookup shortcut that was introduced in the Tiger (Apple + CTRL +D), you'll be able to cross reference any word you come across while viewing files in dictionary-enabled OS X apps. It's similar to what some chat apps (including Trillian) have done, although far more extensible for enterprising developers.
Leopard is also adding a new Web history search to Spotlight, OS X's integrated search tool. Users will be able to search for site names, along with any of the content that was in the pages. This relies on Safari being enabled for history. For users who enjoy similar features from Google's desktop search, this might mean one less app to install, and the potential for this to work with Firefox given the right Spotlight plug-in.
Earlier today Apple announced it'd be releasing Leopard on the 26th, just a week and a half away. More news on that over at Crave.