I'd like to see 2 new features, regarding preferences, and something I call "blocks."
Preferences
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Rather than going to the menu and selecting 'Preferences,' I think it would be neat if each app had an icon similar to the one widgets have. This way, you could click it, and the app would rotate and show the reverse side where all the preference settings could be found.
"Blocks"
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I think it would be neat if apps were integrated into blocks, or "cubes."
For example, there could be an iWork 'cube' or block; opening the application would present you with the usual "what would you like to make: document, presentation, etc" options.
Clicking "presentation" would make the block rotate and expose the side which has the presentation software, Keynote, and all its features.
There would be a new icon that would let you go back to the selection side of the block, or browse to another side, such as the Pages side, in this example.
This could also work for iLife, having iTunes, iPhoto, iMovie, iDVD, iWeb all being "sides" of one cube. Still seperate apps, but the way you access them would change. Opening iTunes would not cause iPhoto and all other iApps to open as well - only browsing to that app's side of the cube would open the app.
Closing the app would cause it to rotate back to the orignal one you opened, or you could browse between sides without closing any that you've opened.
Even further, there could be a 'Create a block' feature, where you could select up to 6 apps and compose your own block and give it a title.
For example, I would like a "Most used" block, which would have Firefox on one side, iTunes on another.
There would be an additional feature which would let you spin and rotate blocks similar to expose' that so you can look at what is on them without accessing each side individualy. Expose' would be revamped to be "block-aware" to show all sides of all blocks when accessed.
It could go even further to introduce 'Smart Blocks' which automatically update to recognize the applications you access most, least, or are related (a photography apps block, a writing block, a web block, etc).
Combining 6 apps into 1 rotatable block would be huge for saving screen space and increasing productivity. Sides of blocks could be 'detached' or unfolded at any time,so you could see two sides next to each other at once.
The uses for this I think would be limitless.