I'm not a developer, but what I know about OS X and it's user interface, most apps would not have to be re-written, because the theme elements are handled by OS X itself (currently in Extras.rsrc on PowerPC machines, and Extras2.rsrc on Intel based Macs) so all Apple would have to do is implement the changes and they would take place system wide, though some minor changes may need to be made to certain 3rd party apps for a more fluid experience. Feel free to correct me if I'm wrong, because like I said I am not a developer myself. As far as the new iPhone (which I doubt will be called 3GS, too similar to iPhone 3G and could easily be confused), it will mostly be under-the-hood changes - faster processor, more RAM, the current 8 GB and 16 GB price point models will be 16 and 32 GB, respectively, video recording (though doubtful a front-facing camera, though possible), better battery life, matte finish on back, pretty much every reliable rumor than has been published about it, it will have. The lower priced model is probably real, but will be like what they did with the new MacBooks - sell the previous model for a lower price, but no major features. So the $99 or $149 model will just be the current model with maybe an extra feature or two.
About Gruber, I think since he allegedly knows so much inside Apple he should be christened MacGruber
About Gruber, I think since he allegedly knows so much inside Apple he should be christened MacGruber