OS X supports a number of menu bar additions (known as "menu extras"), which can be convenient to use; however, you may run into problems where placing your mouse over the icons will give no response and may show the spinning beachball. When this happens, items such as the clock and network graphs will freeze; however, regular applications and the system menus to the left that they use will still function properly.
Not all menu extras are created the same, and there are several ways that developers can implement them. Some run as independent processes, and others are launched and managed by the "SystemUIServer" process, which is loaded by each account upon login to present custom menu items for that user. This problem with the menu items becoming unresponsive is that the SystemUIServer process hangs, causing the menus it is managing to stop functioning. This only affects those the server is managing, and others that run as independent process may still function.
There are a number of reasons why the SystemUIServer could be crashing, including faults in the preference file the server uses, as well as incompatibility with menu items. You can tackle this problem with a few fixes and workarounds.
Log out and Log In
If the server has crashed, you can restart it by logging out and back in. While this is an easy way to get it running again, it will not necessarily address the problem and the server may crash again. Additionally, this will require you to quit all applications, which may be inconvenient for people who are in the middle of working.
Quit and relaunch the SystemUIServer process
An alternative to logging out is to quit the SystemUIServer process. This can be done via "Activity Monitor" by searching for "systemuiserver" and quitting (or force-quitting) the process associated with your username. This can also be done by using the "top" and "kill" commands in the terminal, which may be more successful if Activity Monitor does not work.
Once the process is quit, all the menu extras except for spotlight should disappear. The server should restart automatically; however, if it does not then you can relaunch it manually in the Finder by going to the /System/Library/CoreServices/ folder and launching the SystemUIServer.app process. The menus will return and should function as usual.
Remove the preference file
The server process stores menu items in the file "com.apple.systemuiserver.plist" which is located in the /username/Library/Preferences/ folder. Remove this file from the folder and log out and log in again to restart the server. Keep in mind that doing this will reset the menu extras to the default ones, so you will have to enable them again in various system preferences and applications if the application uses the server for managing the menu.
Remove offending menu items
If removing the preference file and restarting the server does not stop the problem, it may be from an incompatibility with a menu item. The main culprits for this would be third-party menu extras, so start by removing them. In most cases you can hold the command key and drag them off the menu bar; however, some may require you to disable them in the respective application. If this does not work, next try removing the application menu items that come with OS X, such as that for iChat. Finally, disable individual system menu extras such as VPN, Bluetooth, the Displays, and other ones for various system preferences.