After Apple's release of 10.6.2 yesterday, I installed it and as with many people I had no trouble with the update. The updater downloaded and installed without a hitch, and 10.6.2 feels for me very much like previous versions of Snow Leopard. Despite this and other success stories, a number of early adopters have discussed a few minor problems that have cropped up, which include no sound after updating, and issues with the updating process.
No sound after updating
This seems to be the most widespread problem with the 10.6.2 update. After installing and restarting people have found that the system will not output any system sounds whereas some applications seem to be outputting sound just fine. This is primarily because the system has reset the sound output device in the System Preferences, and most people with this problem have been able to tackle it by selecting the proper output device again in the "Sound" system preferences. It seems for these people the update has changed the output to read "Internal Speakers."
Others with this problem have found a fix by downloading and installing the "Combo" updater, which is a more global approach to tackling odd problems that crop up in the update process.
Pausing at the blue screen
A second issue is some users' systems pausing at the blue screen upon rebooting. Apple has mentioned that for 10.6 they put in great effort to avoid hangs the blue screen, but it seems it could still pop up. If you see a blue screen, the first thing to do would be to sit back and wait for it to complete whatever it's doing. Many times people force the system to restart when waiting 5-10 minutes could allow the system to pass this screen and boot normally. In most cases, the blue screen will appear only once, and upon a successful boot will not show again.
If the screen persists, you can try booting off the Snow Leopard DVD and run a permissions repair on the boot drive using Disk Utility. While you're at it you can also run a disk verification and repair. With this done, reboot the system and hold the "Shift" key to get into Safe Mode, and hopefully once you pass the blue screen it will not show up again.
If you are only able to boot into Safe Mode, use the ethernet to connect to the internet (wireless may be disabled) and download and run the "Combo" updater. One suggestion I have is to always download the combo updater and keep it on a DVD somewhere before updating, so you can easily access it in the event of an update error.
Problem updating..."error has occurred"
A number of people have tried updating only to have the process stop half-way through with the warning "An error occurred and the installation cannot be completed". If you are able to install, the first recommendation is to try the combo updater to manually install all the files that have been updated since the initial 10.6.0 release.
Despite this, some people still run into problems with the "combo" updater, but have found that applying the standard "delta" updater seems to work. If you cannot get any updater to install, try running a permissions fix on the boot drive using Disk Utility, and try running the updaters when booted into "Safe" mode. if this does not work, the last suggestion is to reinstall 10.6.0 from the Snow Leopard DVD and then try updating.
Doing this should be straightforward any not require you to change any settings in the installer, and the installer should automatically archive and install your system, and keep your user data and applications. After this is done, try updating the system again. Keep in mind that some applications may need to be reinstalled after you do this, but those that require this should be relatively few.