Spotlight in upper right screen corner in Mountain Lion
Solution 1:
It used to be the realm of the first menu-bar item to start the got the prized first (last?) slot in the menu bar. But since Spotlight, it's always had the prime location to itself. Now it's been usurped. That's not to say that some command line hack won't turn up that can change things, but as things stand there is no officially supported/provided way of doing this via a preference pane.
But I wouldn't actually go looking - the whole point of the spotlight button is to allow you to type in some search criteria. As such, why click the icon, then move to the keyboard - just use the provided keyboard shortcut instead - command+space is not only the easiest to remember (for me) it's also the easiest to pull off even if you are terrible at remembering shortcuts. I use it as my command launcher these days, just command+space+"sa"+return starts Safari up faster than mousework for me.
Solution 2:
This isn't my ideal answer, because it eliminates not only the Notification Center icon, but Notification Center itself. But for anyone desperate to get Spotlight back in the top corner, here goes:
Warning: This involves hacking your System folder; make appropriate backups and proceed with caution!
To disable Notification Center entirely (which will cause its icon to not appear in the Menu Bar), you can go to /System/Library/CoreServices and select Notification Center.app. Press ⌘I to Get Info. Click the Lock icon at the bottom of the screen to unlock the settings (you will be prompted for your password). In the Sharing and Permissions portion of the pane, click the plus sign. Add your account as a special user, then set the Privilege column to Read & Write for yourself. Then, in the Name and Extension field, add the letter x to the beginning of the file name, dismissing any warnings the system throws your way.
Reboot the system.
Note that this eliminates the icon, but also all Notification Center functionality.
Spotlight does, however, return to its proper place. Not worth it for me, but someone might find this helpful.
Solution 3:
Bartender is an app, presently in beta, that allows you to hide the notification center menubar item, among other menu bar-tending tasks. Notification Center is hidden (and so Spotlight is rightmost), but I still get notifications!