Before you blame Apple look to your own systems. They may be the reason for the problems. So, to get you started back to operation you will need to reinstall Snow Leopard as follows:
Reinstall OS X without erasing the drive
Do the following:
1. Repair the Hard Drive and Permissions
Boot from your Snow Leopard Installer disc. After the installer loads select your language and click on the Continue button. When the menu bar appears select Disk Utility from the Utilities menu. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the installer.
If DU reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.
2. Reinstall Snow Leopard
If the drive is OK then quit DU and return to the installer. Proceed with reinstalling OS X. Note that the Snow Leopard installer will not erase your drive or disturb your files. After installing a fresh copy of OS X the installer will move your Home folder, third-party applications, support items, and network preferences into the newly installed system.
Once Snow Leopard has been reinstalled and working download the Mac OS X 10.6.8 Update Combo and install it. Let's see if this doesn't get things going properly.
I have read a number of posts on 10.6.8 issues that have been resolved by disk verification/repair permissions, and will henceforth include those activities as part of my pre-update process (hope I can remember!). Better yet, if Apple built in disk verification/repair permissions as part of the update for forgetful folks like me, that would be great.
This is not the drive. One is a brandnew SSD on my Macbook Pro and I am already running an "emergency" OS on my second partition (that I wisely installed beforehand).
On the other machine, I got 4 drives and running a different OS and Windows and the directory structures on neither are corrupt (for that I can even use target disk mode to mount the respective 10.6.8 OS).
The issue is that 10.6.8. does not work and judging by the posts of others, there are massive issues, and if this is the preparation to OS 10.7 I can say with VERY good authority, that 10.7 does not cause these issues but it IS indeed this update which fails to either disable or update certain kernel extensions.
I have even tried to rename the /Volume/System/Library/CoreServices/SystemVersion.plist successfully where the key is the built, not the version, and successfully re-installed 10.6.7 combo, however on boot, the single user mode (verbose) reports a blank in the OS and fails to boot completely. Since the "framework" reports as "10.7"
I have also installed the combo 10.6.8., and my SSD is now booting back in the loop (at least it now "knows" the framework is correct).
Apple MUST post a fix that can be run either from disk or target mode or another drive.
Thank you for this, C5Z. you are correct, of course, but I have been recommending it for years. See my reply to kappy, it is the update that is faulty.
Before and after any software update, I tend to quit all apps and run DU / repair disk permissions. I also do after e.g. "tinkering" trying to make a system work (as below).
After a painful two days (and NO backup!!! tested on two machines), I have managed to re-install OSX 10.6.7:
1) boot from OSX Snow Leopard disc (the one from the Box set)./ Macbook Pro Install disc 10.6.3
2) install OS 10.6.x with "customize" selected to run ONLY the greyed out minimum requirements onto the faulty 10.6.8 disk.
4) voila: the old (10.6.x) user account was back with ALL files and folders and applications (including mail etc, so all preferences were intact!)
5) run disk permissions repair
6) run software update EXCEPT 10.6.8
7) install 10.6.7 combo (standalone)
8) repair disk permissions
9) run software update (it will bring up Java update)
system restored - above steps correct as at 28th June 2011.
Thank you for reporting back Alexandre. We had one failed update out of four users here. Safe Boot didn't work, and it wasn't getting very far at all...stuck after loading bluetooth drivers. I was going to do a fresh install and migrate the user's account, but this did the trick so far, and I'm running the Java update now.