The notification center in the new Mac OSX Mountain Lion is a nice step toward notification unification but in my mind it's a long way off from where it needs to be. The problem with the new notification center is that it's an isolated design. It hasn't taken into consideration how to eliminate a lot of the cruft that has accumulated in OSX.
The Mac Shell/Chrome should provide a unified view of launching, viewing and managing applications.
The notification center doesn't feel like it should be along the right hand edge of the screen, it feels like it should be on the left hand edge. The notification center is most closely associated with the dashboard concept. Docking notification to the right makes sense if you're a third party app like growl and have no choice but the OS can break this limitation and put itself in prime position.
The Apple meny is fairly useless for a beginner and replacing it with something like the notification center is a much better use of screen space. The key actions from this menu are preserved. More obscure menu items are duplicated in other parts of the system.
I experimented with adding menu items near the Apple Menu but on deeper consideration I felt it wasn't necessary. System Information can be launched and has all the same "About this Mac" info. The App Store has it's own icon in the dock. The finder has its own Recent menu. Advanced users could be satisfied with an advanced ⌘+Click combo to reveal the original meny style..
Siri & Search & Spotlight
While the long-term path is likely to introduce Siri into the OS, the first step of that should be dictation/search. The spotlight system could use a visual overhaul and integration into the side-bar made a lot of sense. Similar to the notification center it seemed like searching was a launching action and could live within the notification area along the left. Typing a search would replace the notifications with search results.
It should be noted that on iOS a similar unification unification should be done. The search on iOS is hidden to the left of the 1st screen while the notification area is hidden above the screen, Siri is hidden below all screens. Rather then using all the edges we can simplify the model entirely.
The OS still has widgets? Yes and they are done fairly poorly. Widgets should be light weight and allow you to get key information and then get out of the way. Items like stocks & weather, are arguably persistent notifications and hence could live in the notification center.
The full widgets screen could also be tied into the notification metaphor using gestures. Pull to the right a little and the notification center. Pull a little further and the whole widget screen slides in. Things like twitter would be a notification widget, not something special.
Logout / Shutdown
Yep, just matching the visual style of the login screen. Hold down option and your shutdown item becomes a "Restart." I've never intentionally restarted, usually it's an install/update that forces the issue but I'm sure someone wants it.