So Jimmy G has an idea: why not add Cover Flow functionality into Safari? You could browse updated versions of your bookmarks just like you browse your albums in iTunes. I'm not sure I'd implement it exactly the way he has (click the pic above to see a bigger version), as if I'm browsing my web visually, I'd rather more real estate was given to the pages themselves. But it's an interesting idea.
And I think we could use a little more color in the web browsing experience-- the space between the browser tabs, if you will. If you're a Firefox for Windows user you really should try out the Tab Effect**; it lets you flip between tabs like a rotating cube. It's actually a little much to use all the time, but it's a cool idea, at least. And the PicLens plugin for Safari also puts a little oomph in your picture browsing-- it can create slideshows of Flickr pictures with just a click. You may think it's superfluous (and yes, if your app doesn't function already, it is) but we all need a little bit of eye candy now and again.
**Whoops. As commenter Rae notices, Tab Effect is Windows only, because it requires Directx 8. But it's still a cool effect.