After updating your OS you may find a number of small issues with programs not functioning properly or some system services not working. As we noted earlier, some people have had difficulty with iTunes freezing after updating to OS X 10.6.7, but in addition some other people have found their Bluetooth devices such as the Magic Mouse and Magic Trackpad have not been able to connect.
When these types of issues occur, sometimes basic resets can clear the problem and cause the system to properly recognize the available services. The basic resets are to restart the computer (using Safe Mode and then restarting normally as an optional step), reset the PRAM, and reset the SMC.
A basic restart is fairly straightforward, but to get to Safe Mode you will need to press and hold the Shift key after the boot chimes and until the gray Apple boot screen appears. After the system finishes booting to Safe Mode, restart it again normally.
To reset the PRAM, restart the system and immediately hold down the Option-Command-P-R keys all at once after hearing the boot chimes. Hold these keys and wait for the system to cycle through a few resets (you should hear the boot chimes each time). Then release the keys and allow the system to boot normally.
The last option is to reset the System Management Controller (SMC), which is responsible for handling power, peripheral lights, buttons, and various system sensors. The process for resetting the SMC will depend on the specific Mac model you have, so be sure to check Apple's SMC reset instructions for information on how to do this with your Mac. In the case of Bluetooth devices not being recognized, people have found the SMC reset fixed the issue.
These resets can help fix odd problems after an update; however, do not do them if your system is working fine. While performing these resets will not harm anything, sometimes they can cause system settings and behaviors to revert to default.