I've mentioned this many times before, but it would be awesome if a sliding gesture (up and/or down) brought up different tiers of UI capabilities. When you swipe up or down, you'd get to a specific functional tier...once on that particular row (tier)...you then swipe left and right to as you do now.
You could have endless possibilities with multiple tiers of home screen rows. One row could be for apps like we have now. Then swipe left and right just as we do now to browse through that row (apps in this case). Swipe up to reach full screen apps running in the background, another swipe up for notifications, another for dashboard widgets. At each row, you can swipe left and right to see more within the theme of that particular row. To make it completely awesome, the user can customize which rows are primary, secondary, tertiary, etc.
Think about that. Most people would have the primary row set as their dashboard (widgets). A widget to turn on bluetooth, see appointments, weather, etc. Swipe left and right to manage and view all your widgets (12 pages of widgets). A swipe down brings up notifications. A swipe up brings the normal icons (app) row. Another swipe up brings full screen apps (safari, Music, Videos, mail, etc). Another swipe up brings together all your social networking pages. Another brings up iCloud functionality. Again, at each level you have the capability to swipe left/right to browse within that theme. This would maintain the Apple-ness of the OS and expand on the iOS capability.
To me it's like browsing the the App Store on your iPhone. Your reading about a particular app until you get to the pictures, then you can swipe left and right to see the apps pictures.